Howmet Aerospace (HWM) 10-K 26 Feb 18 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2017	Feb. 16, 2018	Jun. 30, 2017
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Trading Symbol	ARNC
Entity Registrant Name	Arconic Inc.
Entity Central Index Key	4,281
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		482,772,252
Entity Public Float			$ 10

Statement of Consolidated Opera

Statement of Consolidated Operations - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
Sales (N)	$ 12,960	$ 12,394	$ 12,413
Cost of goods sold (exclusive of expenses below)	10,357	9,811	10,104
Selling, general administrative, and other expenses (C)	731	942	765
Research and development expenses	111	132	169
Provision for depreciation and amortization	551	535	508
Impairment of goodwill (A and E)	719	0	25
Restructuring and other charges (D)	165	155	214
Operating income	326	819	628
Interest expense (S)	496	499	473
Other income, net (L)	640	94	28
Income from continuing operations before income taxes	470	414	183
Provision for income taxes (Q)	544	1,476	339
Loss from continuing operations after income taxes	(74)	(1,062)	(156)
Income (loss) from discontinued operations after income taxes (C)	0	184	(41)
Net loss	(74)	(878)	(197)
Less: Net income from continuing operations attributable to noncontrolling interests	0	0	1
Less: Net income from discontinued operations attributable to noncontrolling interests (C)	0	63	124
Net loss attributable to Arconic	(74)	(941)	(322)
Amounts Attributable to Arconic Common Shareholders (P):
Net loss	$ (127)	$ (1,010)	$ (391)
(Loss) earnings per share—basic:
Continuing operations (in usd per share)	$ (0.28)	$ (2.58)	$ (0.54)
Discontinued operations (in usd per share)	0	0.27	(0.39)
Net loss per share-basic (in usd per share)	(0.28)	(2.31)	(0.93)
(Loss) earnings per share—diluted
Continuing operations (in usd per share)	(0.28)	(2.58)	(0.54)
Discontinued operations (in usd per share)	0	0.27	(0.39)
Net loss per share-diluted (in usd per share)	$ (0.28)	$ (2.31)	$ (0.93)

Statement of Consolidated Compr

Statement of Consolidated Comprehensive (Loss) Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net (loss) income	$ (74)	$ (878)	$ (197)
Other comprehensive (loss) income, net of tax (B):
Change in unrecognized net actuarial loss and prior service cost/benefit related to pension and other postretirement benefits	(220)	(482)	(2)
Foreign currency translation adjustments	254	450	(1,995)
Net change in unrealized gains on available-for-sale securities	(134)	137	(5)
Net change in unrecognized gains (losses) on cash flow hedges	26	(612)	826
Total Other comprehensive (loss) income, net of tax	(74)	(507)	(1,176)
Comprehensive (loss) income	(148)	(1,385)	(1,373)
Arconic
Net (loss) income	(74)	(941)	(322)
Other comprehensive (loss) income, net of tax (B):
Change in unrecognized net actuarial loss and prior service cost/benefit related to pension and other postretirement benefits	(220)	(479)	(10)
Foreign currency translation adjustments	252	268	(1,566)
Net change in unrealized gains on available-for-sale securities	(134)	137	(5)
Net change in unrecognized gains (losses) on cash flow hedges	26	(617)	827
Total Other comprehensive (loss) income, net of tax	(76)	(691)	(754)
Comprehensive (loss) income	(150)	(1,632)	(1,076)
Noncontrolling Interests
Net (loss) income	0	63	125
Other comprehensive (loss) income, net of tax (B):
Change in unrecognized net actuarial loss and prior service cost/benefit related to pension and other postretirement benefits	0	(3)	8
Foreign currency translation adjustments	2	182	(429)
Net change in unrealized gains on available-for-sale securities	0	0	0
Net change in unrecognized gains (losses) on cash flow hedges	0	5	(1)
Total Other comprehensive (loss) income, net of tax	2	184	(422)
Comprehensive (loss) income	$ 2	$ 247	$ (297)

Consolidated Balance Sheet

Consolidated Balance Sheet - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents (U)	$ 2,150	$ 1,863
Receivables from customers, less allowances of $8 in 2017 and $13 in 2016 (R)	1,035	974
Other receivables (C and R)	339	477
Inventories (G)	2,480	2,253
Prepaid expenses and other current assets	374	325
Total current assets	6,378	5,892
Properties, plants, and equipment, net (H)	5,594	5,499
Goodwill (A and E)	4,535	5,148
Deferred income taxes (Q)	743	1,234
Investment in common stock of Alcoa Corporation (C and U)	0	1,020
Intangibles, net (E)	987	988
Other noncurrent assets	481	257
Total Assets	18,718	20,038
Current liabilities:
Accounts payable, trade	1,839	1,744
Accrued compensation and retirement costs	399	398
Taxes, including income taxes	75	85
Accrued interest payable	124	153
Other current liabilities	349	329
Short-term debt (I and U)	38	40
Total current liabilities	2,824	2,749
Long-term debt, less amount due within one year (I and U)	6,806	8,044
Accrued pension benefits (T)	2,564	2,345
Accrued other postretirement benefits (T)	841	889
Other noncurrent liabilities and deferred credits (J)	759	870
Total liabilities	13,794	14,897
Arconic shareholders’ equity:
Preferred stock (O)	55	55
Mandatory convertible preferred stock (O)	0	3
Common stock (O)	481	438
Additional capital	8,266	8,214
Accumulated deficit	(1,248)	(1,027)
Accumulated other comprehensive loss (B)	(2,644)	(2,568)
Total Arconic shareholders’ equity	4,910	5,115
Noncontrolling interests	14	26
Total equity	4,924	5,141
Total Liabilities and Equity	$ 18,718	$ 20,038

Consolidated Balance Sheet (Par

Consolidated Balance Sheet (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Receivables from customers, allowance	$ 8	$ 13

Statement of Consolidated Cash

Statement of Consolidated Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash from Operations
Net (loss) income	$ (74)	$ (878)	$ (197)
Adjustments to reconcile net loss to cash from operations:
Depreciation, depletion and amortization	551	1,132	1,280
Deferred income taxes	434	1,125	34
Equity income, net of dividends	0	42	158
Impairment of goodwill (A and E)	719	0	25
Restructuring and other charges	165	257	1,195
Net gain from investing activities—asset sales	(513)	(156)	(74)
Net periodic pension benefit cost	217	304	485
Stock-based compensation	67	86	92
Excess tax benefits from stock-based payment arrangements	0	0	(9)
Other	61	60	(32)
Changes in assets and liabilities, excluding effects of acquisitions, divestitures, and foreign currency translation adjustments:
(Increase) decrease in receivables	(124)	(238)	212
(Increase) in inventories	(192)	(29)	(64)
Decrease (increase) in prepaid expenses and other current assets	11	(76)	46
Increase (decrease) in accounts payable, trade	62	232	(90)
(Decrease) in accrued expenses	(116)	(394)	(437)
(Decrease) increase in taxes, including income taxes	(23)	93	25
Pension contributions	(310)	(290)	(470)
(Increase) in noncurrent assets	(41)	(152)	(370)
(Decrease) in noncurrent liabilities	(193)	(248)	(227)
Cash provided from operations	701	870	1,582
Financing Activities
Net change in short-term borrowings (original maturities of three months or less)	(2)	(3)	(16)
Additions to debt (original maturities greater than three months)	816	1,962	1,901
Payments on debt (original maturities greater than three months)	(1,634)	(2,734)	(2,030)
Proceeds from exercise of employee stock options	50	4	25
Excess tax benefits from stock-based payment arrangements	0	0	9
Dividends paid to shareholders	(162)	(228)	(223)
Distributions to noncontrolling interests	(14)	(226)	(106)
Contributions from noncontrolling interests	0	51	2
Net cash transferred from Alcoa Corporation at separation	0	421	0
Other	(17)	(1)	(3)
Cash used for financing activities	(963)	(754)	(441)
Investing Activities
Capital expenditures	(596)	(1,125)	(1,180)
Acquisitions, net of cash acquired (F and M)	0	10	97
Proceeds from the sale of assets and businesses (M)	(9)	692	112
Additions to investments	(2)	(52)	(134)
Sales of investments (C and M)	890	280	40
Net change in restricted cash	12	14	(20)
Other (C)	245	16	25
Cash provided from (used for) investing activities	540	(165)	(1,060)
Effect of exchange rate changes on cash and cash equivalents	9	(7)	(39)
Net change in cash and cash equivalents	287	(56)	42
Cash and cash equivalents at beginning of year	1,863	1,919	1,877
Cash and cash equivalents at end of year	$ 2,150	$ 1,863	$ 1,919

Statement of Changes in Consoli

Statement of Changes in Consolidated Equity - USD ($) $ in Millions	Total	Preferred Class A	Preferred Class B	Preferred stock	Mandatory convertible preferred stock	Common stock	Additional capital	Retained earnings (deficit)	Retained earnings (deficit)Preferred Class A	Retained earnings (deficit)Preferred Class B	Treasury stock	Accumulated Other Comprehensive Loss	Noncontrolling Interests
Balance at beginning of period at Dec. 31, 2014	$ 14,794			$ 55	$ 3	$ 1,304	$ 9,284	$ 9,379			$ (3,042)	$ (4,677)	$ 2,488
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income	(197)							(322)					125
Other comprehensive loss (B)	(1,176)											(754)	(422)
Cash dividends declared:
Cash dividends declared, preferred		$ (2)	$ (67)						$ (2)	$ (67)
Cash dividends declared, common	(154)							(154)
Equity option on convertible notes (F)	55						55
Stock-based compensation (O)	92						92
Common stock issued: compensation plans (O)	22						(195)				217
Issuance of common stock (F and O)	870					87	783
Distributions	(106)												(106)
Contributions	2												2
Other	(2)
Balance at end of period at Dec. 31, 2015	14,131			55	3	1,391	10,019	8,834			(2,825)	(5,431)	2,085
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income	(878)							(941)					63
Other comprehensive loss (B)	(507)											(691)	184
Cash dividends declared:
Cash dividends declared, preferred		(2)	(67)						(2)	(67)
Cash dividends declared, common	(159)							(159)
Stock-based compensation (O)	86						86
Common stock issued: compensation plans (O)	(19)						(205)				186
Distributions	(226)												(226)
Contributions	51												51
Retirement of Treasury stock (O)	0					(76)	(2,563)				2,639
Reverse stock split (O)	0					(877)	877
Distribution of Alcoa Corporation	(7,271)							(8,692)				3,554	(2,133)
Other	2												2
Balance at end of period at Dec. 31, 2016	5,141			55	3	438	8,214	(1,027)			0	(2,568)	26
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income	(74)							(74)					0
Other comprehensive loss (B)	(74)											(76)	2
Cash dividends declared:
Cash dividends declared, preferred		$ (2)	$ (51)						$ (2)	$ (51)
Cash dividends declared, common	(109)							(109)
Stock-based compensation (O)	67						67
Common stock issued: compensation plans (O)	21						21
Issuance of common stock (F and O)	4					4
Distributions	(14)												(14)
Conversion of mandatory convertible preferred stock (O)	0				(3)	39	(36)
Other	15							15					0
Balance at end of period at Dec. 31, 2017	$ 4,924			$ 55	$ 0	$ 481	$ 8,266	$ (1,248)			$ 0	$ (2,644)	$ 14

Statement of Changes in Consol8

Statement of Changes in Consolidated Equity (Parenthetical) - $ / shares	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Common Stock, dividends declared per share (usd per share)	$ 0.06	$ 0.24	$ 0.36	$ 0.12
Preferred Class A
Preferred, dividends per share (usd per share)		3.75	3.75	3.75
Preferred Class B
Preferred, dividends per share (usd per share)		$ 20.1563	$ 26.875	$ 26.8750

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Basis of Presentation. The Consolidated Financial Statements of Arconic Inc. and subsidiaries (“Arconic” or the “Company”) are prepared in conformity with accounting principles generally accepted in the United States of America (GAAP) and require management to make certain judgments, estimates, and assumptions. These may affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the financial statements. They also may affect the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates upon subsequent resolution of identified matters. Certain prior year amounts have been reclassified to conform to the current year presentation. The separation of Alcoa Inc. into two standalone, publicly-traded companies, Arconic Inc. (the new name for Alcoa Inc.) and Alcoa Corporation, became effective on November 1, 2016 (the “Separation Transaction”). The financial results of Alcoa Corporation for all periods prior to the Separation Transaction have been retrospectively reflected in the Statement of Consolidated Operations as discontinued operations and, as such, have been excluded from continuing operations and segment results for all periods presented prior to the Separation Transaction. The cash flows and comprehensive income related to Alcoa Corporation have not been segregated and are included in the Statement of Consolidated Cash Flows and Statement of Consolidated Comprehensive (Loss) Income, respectively, for all periods presented. See Note C for additional information related to the Separation Transaction and discontinued operations. Principles of Consolidation. The Consolidated Financial Statements include the accounts of Arconic and companies in which Arconic has a controlling interest. Intercompany transactions have been eliminated. Investments in affiliates in which Arconic cannot exercise significant influence are accounted for on the cost method. Management also evaluates whether an Arconic entity or interest is a variable interest entity and whether Arconic is the primary beneficiary. Consolidation is required if both of these criteria are met. Arconic does not have any variable interest entities requiring consolidation. Related Party Transactions. Arconic buys products from and provides services to Alcoa Corporation following the separation at negotiated prices between the parties. These transactions were not material to the financial position or results of operations of Arconic for all periods presented. Effective May 2017, upon disposition of the remaining common stock that Arconic held in Alcoa Corporation, they are no longer deemed a related party. Cash Equivalents. Cash equivalents are highly liquid investments purchased with an original maturity of three months or less. Inventory Valuation. Inventories are carried at the lower of cost and net realizable value, with cost for approximately half of U.S. inventories determined under the last-in, first-out (LIFO) method. The cost of other inventories is determined under a combination of the first-in, first-out (FIFO) and average-cost methods. Properties, Plants, and Equipment. Properties, plants, and equipment are recorded at cost. Depreciation is recorded principally on the straight-line method at rates based on the estimated useful lives of the assets. The following table details the weighted-average useful lives of structures and machinery and equipment by reporting segment (numbers in years): Segment Structures Machinery and equipment Engineered Products and Solutions 29 17 Global Rolled Products 31 21 Transportation and Construction Solutions 27 18 Gains or losses from the sale of assets are generally recorded in Other income, net (see policy below for assets classified as held for sale and discontinued operations). Repairs and maintenance are charged to expense as incurred. Interest related to the construction of qualifying assets is capitalized as part of the construction costs. Properties, plants, and equipment are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of such assets (asset group) may not be recoverable. Recoverability of assets is determined by comparing the estimated undiscounted net cash flows of the operations related to the assets (asset group) to their carrying amount. An impairment loss would be recognized when the carrying amount of the assets (asset group) exceeds the estimated undiscounted net cash flows. The amount of the impairment loss to be recorded is calculated as the excess of the carrying value of the assets (asset group) over their fair value, with fair value determined using the best information available, which generally is a discounted cash flow (DCF) model. The determination of what constitutes an asset group, the associated estimated undiscounted net cash flows, and the estimated useful lives of assets also require significant judgments. See Note F for information regarding asset impairments. Goodwill. Goodwill is not amortized; instead, it is reviewed for impairment annually (in the fourth quarter) or more frequently if indicators of impairment exist or if a decision is made to sell or realign a business. A significant amount of judgment is involved in determining if an indicator of impairment has occurred. Such indicators may include deterioration in general economic conditions, negative developments in equity and credit markets, adverse changes in the markets in which an entity operates, increases in input costs that have a negative effect on earnings and cash flows, or a trend of negative or declining cash flows over multiple periods, among others. The fair value that could be realized in an actual transaction may differ from that used to evaluate the impairment of goodwill. Goodwill is allocated among and evaluated for impairment at the reporting unit level, which is defined as an operating segment or one level below an operating segment. Arconic has eight reporting units, of which four are included in the Engineered Products and Solutions segment, three are included in the Transportation and Construction Solutions segment, and the remaining reporting unit is the Global Rolled Products segment. More than 85% of Arconic’s total goodwill at December 31, 2017 is allocated to two reporting units as follows: Arconic Fastening Systems and Rings (AFSR) ( $2,221 ) and Arconic Power and Propulsion (APP) ( $1,686 ) businesses, both of which are included in the Engineered Products and Solutions segment. These amounts include an allocation of Corporate’s goodwill. In reviewing goodwill for impairment, an entity has the option to first assess qualitative factors to determine whether the existence of events or circumstances leads to a determination that it is more likely than not (greater than 50% ) that the estimated fair value of a reporting unit is less than its carrying amount. If an entity elects to perform a qualitative assessment and determines that an impairment is more likely than not, the entity is then required to perform the quantitative impairment test (described below), otherwise no further analysis is required. An entity also may elect not to perform the qualitative assessment and, instead, proceed directly to the quantitative impairment test. The ultimate outcome of the goodwill impairment review for a reporting unit should be the same whether an entity chooses to perform the qualitative assessment or proceeds directly to the quantitative impairment test. Arconic determines annually, based on facts and circumstances, which of its reporting units will be subject to the qualitative assessment. For those reporting units where a qualitative assessment is either not performed or for which the conclusion is that an impairment is more likely than not, a quantitative impairment test will be performed. Arconic’s policy is that a quantitative impairment test be performed for each reporting unit at least once during every three -year period. Under the qualitative assessment, various events and circumstances (or factors) that would affect the estimated fair value of a reporting unit are identified (similar to impairment indicators above). These factors are then classified by the type of impact they would have on the estimated fair value using positive, neutral, and adverse categories based on current business conditions. Additionally, an assessment of the level of impact that a particular factor would have on the estimated fair value is determined using high, medium, and low weighting. Furthermore, management considers the results of the most recent quantitative impairment test completed for a reporting unit and compares the weighted average cost of capital (WACC) between the current and prior years for each reporting unit. During the 2017 annual review of goodwill, management performed the qualitative assessment for one reporting unit, Arconic Wheel and Transportation Products (within the Transportation and Construction Solutions segment). Management concluded that it was not more likely than not that the estimated fair value of the reporting unit was less than its carrying value. As such, no further analysis was required. Under the quantitative impairment test, the evaluation of impairment involves comparing the current fair value of each reporting unit to its carrying value, including goodwill. Arconic uses a discounted cash flow model (DCF) to estimate the current fair value of its reporting units when testing for impairment, as management believes forecasted cash flows are the best indicator of such fair value. A number of significant assumptions and estimates are involved in the application of the DCF model to forecast operating cash flows, including markets and market share, sales volumes and prices, production costs, tax rates, capital spending, discount rate, and working capital changes. Most of these assumptions vary significantly among the reporting units. Cash flow forecasts are generally based on approved business unit operating plans for the early years and historical relationships in later years. The WACC rate for the individual reporting units is estimated with the assistance of valuation experts. Arconic would recognize an impairment charge for the amount by which the carrying amount exceeds the reporting unit’s fair value without exceeding the total amount of goodwill allocated to that reporting unit. During the 2017 annual review of goodwill, management proceeded directly to the quantitative impairment test for six reporting units as follows: AFSR, APP, Arconic Titanium and Engineered Products (ATEP), and Arconic Forgings and Extrusions (AFE), which are all included in the Engineered Products and Solutions segment, Global Rolled Products, and Building and Construction Systems, which is included in the Transportation and Construction Solutions segment. The estimated fair value for five of the six reporting units exceeded its respective carrying value, resulting in no impairment. However, the estimated fair value of AFE was lower than its carrying value. As such, in the fourth quarter of 2017, Arconic recorded an impairment for the full amount of goodwill in the AFE reporting unit of $719 . The decrease in the AFE fair value was primarily due to unfavorable performance that is impacting operating margins and a higher discount rate due to an increase in the risk-free rate of return, while the carrying value increased compared to prior year. Goodwill impairment tests in 2016 and 2015 indicated that goodwill was not impaired for any of the Company’s reporting units, except for the soft alloy extrusion business in Brazil which is included in the Transportation and Construction Solutions segment. In the fourth quarter of 2015, for the soft alloy extrusion business in Brazil, the estimated fair value as determined by the DCF model was lower than the associated carrying value of its reporting unit’s goodwill. As a result, management determined that the implied fair value of the reporting unit’s goodwill was zero . Arconic recorded a goodwill impairment of $25 in 2015. The impairment of goodwill resulted from headwinds from the downturn in the Brazilian economy and the continued erosion of gross margin despite the execution of cost reduction strategies. As a result of the goodwill impairment, there is no goodwill remaining for the reporting unit. Other Intangible Assets. Intangible assets with indefinite useful lives are not amortized while intangible assets with finite useful lives are amortized generally on a straight-line basis over the periods benefited. The following table details the weighted-average useful lives of software and other intangible assets by reporting segment (numbers in years): Segment Software Other intangible assets Engineered Products and Solutions 6 34 Global Rolled Products 6 9 Transportation and Construction Solutions 5 16 Revenue Recognition. Arconic recognizes revenues when title, ownership, and risk of loss pass to the customer, all of which occurs upon shipment or delivery of the product and is based on the applicable shipping terms. The shipping terms vary across all businesses and depend on the product, the country of origin, and the type of transportation (truck, train, or vessel). In certain circumstances, Arconic receives advanced payments from its customers for product to be delivered in future periods. These advanced payments are recorded as deferred revenue until the product is delivered and title and risk of loss have passed to the customer in accordance with the terms of the contract. Deferred revenue is included in Other current liabilities and Other noncurrent liabilities and deferred credits on the accompanying Consolidated Balance Sheet. Environmental Matters. Expenditures for current operations are expensed or capitalized, as appropriate. Expenditures relating to existing conditions caused by past operations, which will not contribute to future revenues, are expensed. Liabilities are recorded when remediation costs are probable and can be reasonably estimated. The liability may include costs such as site investigations, consultant fees, feasibility studies, outside contractors, and monitoring expenses. Estimates are generally not discounted or reduced by potential claims for recovery. Claims for recovery are recognized when probable and as agreements are reached with third parties. The estimates also include costs related to other potentially responsible parties to the extent that Arconic has reason to believe such parties will not fully pay their proportionate share. The liability is continuously reviewed and adjusted to reflect current remediation progress, prospective estimates of required activity, and other factors that may be relevant, including changes in technology or regulations. Litigation Matters. For asserted claims and assessments, liabilities are recorded when an unfavorable outcome of a matter is deemed to be probable and the loss is reasonably estimable. Management determines the likelihood of an unfavorable outcome based on many factors such as the nature of the matter, available defenses and case strategy, progress of the matter, views and opinions of legal counsel and other advisors, applicability and success of appeals processes, and the outcome of similar historical matters, among others. Once an unfavorable outcome is deemed probable, management weighs the probability of estimated losses, and the most reasonable loss estimate is recorded. If an unfavorable outcome of a matter is deemed to be reasonably possible, then the matter is disclosed and no liability is recorded. With respect to unasserted claims or assessments, management must first determine that the probability that an assertion will be made is likely, then, a determination as to the likelihood of an unfavorable outcome and the ability to reasonably estimate the potential loss is made. Legal matters are reviewed on a continuous basis to determine if there has been a change in management’s judgment regarding the likelihood of an unfavorable outcome or the estimate of a potential loss. Income Taxes. The provision for income taxes is determined using the asset and liability approach of accounting for income taxes. Under this approach, the provision for income taxes represents income taxes paid or payable (or received or receivable) for the current year plus the change in deferred taxes during the year. Deferred taxes represent the future tax consequences expected to occur when the reported amounts of assets and liabilities are recovered or paid, and result from differences between the financial and tax bases of Arconic’s assets and liabilities and are adjusted for changes in tax rates and tax laws when enacted. Valuation allowances are recorded to reduce deferred tax assets when it is more likely than not that a tax benefit will not be realized. In evaluating the need for a valuation allowance, management considers all potential sources of taxable income, including income available in carryback periods, future reversals of taxable temporary differences, projections of taxable income, and income from tax planning strategies, as well as all available positive and negative evidence. Positive evidence includes factors such as a history of profitable operations, projections of future profitability within the carryforward period, including from tax planning strategies, and Arconic’s experience with similar operations. Existing favorable contracts and the ability to sell products into established markets are additional positive evidence. Negative evidence includes items such as cumulative losses, projections of future losses, or carryforward periods that are not long enough to allow for the utilization of a deferred tax asset based on existing projections of income. Deferred tax assets for which no valuation allowance is recorded may not be realized upon changes in facts and circumstances, resulting in a future charge to establish a valuation allowance. Existing valuation allowances are re-examined under the same standards of positive and negative evidence. If it is determined that it is more likely than not that a deferred tax asset will be realized, the appropriate amount of the valuation allowance, if any, is released. Deferred tax assets and liabilities are also re-measured to reflect changes in underlying tax rates due to law changes and the granting and lapse of tax holidays. Tax benefits related to uncertain tax positions taken or expected to be taken on a tax return are recorded when such benefits meet a more likely than not threshold. Otherwise, these tax benefits are recorded when a tax position has been effectively settled, which means that the statute of limitations has expired or the appropriate taxing authority has completed their examination even though the statute of limitations remains open. Interest and penalties related to uncertain tax positions are recognized as part of the provision for income taxes and are accrued beginning in the period that such interest and penalties would be applicable under relevant tax law until such time that the related tax benefits are recognized. Stock-based Compensation. Arconic recognizes compensation expense for employee equity grants using the non-substantive vesting period approach, in which the expense is recognized ratably over the requisite service period based on the grant date fair value. Forfeitures are accounted for as they occur. The fair value of new stock options is estimated on the date of grant using a lattice-pricing model. The fair value of performance awards containing a market condition is valued using a Monte Carlo valuation model. Determining the fair value at the grant date requires judgment, including estimates for the average risk-free interest rate, dividend yield, volatility, and exercise behavior. These assumptions may differ significantly between grant dates because of changes in the actual results of these inputs that occur over time. Most plan participants can choose whether to receive their award in the form of stock options, stock awards, or a combination of both. This choice is made before the grant is issued and is irrevocable. Foreign Currency. The local currency is the functional currency for Arconic’s significant operations outside the United States, except for certain operations in Canada and Russia, where the U.S. dollar is used as the functional currency. The determination of the functional currency for Arconic’s operations is made based on the appropriate economic and management indicators. Acquisitions. Arconic’s business acquisitions are accounted for using the acquisition method. The purchase price is allocated to the assets acquired and liabilities assumed based on their estimated fair values. Any excess purchase price over the fair value of the net assets acquired is recorded as goodwill. For all acquisitions, operating results are included in the Statement of Consolidated Operations from the date of the acquisition. Discontinued Operations and Assets Held For Sale. For those businesses where management has committed to a plan to divest, each business is valued at the lower of its carrying amount or estimated fair value less cost to sell. If the carrying amount of the business exceeds its estimated fair value, an impairment loss is recognized. Fair value is estimated using accepted valuation techniques such as a DCF model, valuations performed by third parties, earnings multiples, or indicative bids, when available. A number of significant estimates and assumptions are involved in the application of these techniques, including the forecasting of markets and market share, sales volumes and prices, costs and expenses, and multiple other factors. Management considers historical experience and all available information at the time the estimates are made; however, the fair value that is ultimately realized upon the divestiture of a business may differ from the estimated fair value reflected in the Consolidated Financial Statements. Depreciation and amortization expense is not recorded on assets of a business to be divested once they are classified as held for sale. Businesses to be divested are generally classified in the Consolidated Financial Statements as either discontinued operations or held for sale. For businesses classified as discontinued operations, the balance sheet amounts and results of operations are reclassified from their historical presentation to assets and liabilities of discontinued operations on the Consolidated Balance Sheet and to discontinued operations on the Statement of Consolidated Operations, respectively, for all periods presented. The gains or losses associated with these divested businesses are recorded in discontinued operations on the Statement of Consolidated Operations. The Statement of Consolidated Cash Flows is not required to be reclassified for discontinued operations for any period. Segment information does not include the assets or operating results of businesses classified as discontinued operations for all periods presented. These businesses are expected to be disposed of within one year . For businesses classified as held for sale that do not qualify for discontinued operations treatment, the balance sheet and cash flow amounts are reclassified from their historical presentation to assets and liabilities of operations held for sale for all periods presented. The results of operations continue to be reported in continuing operations. The gains or losses associated with these divested businesses are recorded in Restructuring and other charges on the Statement of Consolidated Operations. The segment information includes the assets and operating results of businesses classified as held for sale for all periods presented. Recently Adopted Accounting Guidance. On January 1, 2017, Arconic adopted changes issued by the Financial Accounting Standards Board (“FASB”) to employee share-based payment accounting. Previously, an entity determined for each share-based payment award whether the difference between the deduction for tax purposes and the compensation cost recognized for financial reporting purposes resulted in either an excess tax benefit or a tax deficiency. Excess tax benefits were recognized in additional paid-in capital; tax deficiencies were recognized either as an offset to accumulated excess tax benefits, if any, or in the income statement. Excess tax benefits were not recognized until the deduction reduced taxes payable. The changes require all excess tax benefits and tax deficiencies related to share-based payment awards to be recognized as income tax expense or benefit in the Statement of Consolidated Operations. The tax effects of exercised or vested awards should be treated as discrete items in the reporting period in which they occur. An entity also should recognize excess tax benefits regardless of whether the benefit reduces taxes payable in the current period. In addition, the presentation of excess tax benefits related to share-based payment awards in the statement of cash flows changed. Previously, excess tax benefits were separated from other income tax cash flows and classified as a financing activity. The changes require excess tax benefits to be classified along with other income tax cash flows as an operating activity. Also, the changes require cash paid by an employer when directly withholding shares for tax-withholding purposes to be classified as a financing activity. Further, for a share-based award to qualify for equity classification it previously could not be partially settled in cash in-excess of the employer’s minimum statutory withholding requirements. The changes permit equity classification of share-based awards for withholdings up to the maximum statutory tax rates in applicable jurisdictions. The prospective transition method was utilized for excess tax benefits in the Statement of Consolidated Cash Flows. Management determined that the adoption of this guidance did not have a material impact on the Consolidated Financial Statements. On January 1, 2017, Arconic adopted changes issued by the FASB eliminating the requirement for an investor to adjust an equity method investment, results of operations, and retained earnings retroactively on a step-by-step basis as if the equity method had been in effect during all previous periods that the investment had been held as a result of an increase in the level of ownership interest or degree of influence. In addition, an entity that has an available-for-sale equity security that becomes qualified for the equity method of accounting must recognize through earnings the unrealized holding gain or loss in accumulated other comprehensive income at the date the investment becomes qualified for use of the equity method. Management determined that the adoption of this guidance had no impact on the Consolidated Financial Statements. On January 1, 2017, Arconic adopted changes issued by the FASB to derivative instruments designated as hedging instruments. These changes clarify that a change in the counterparty to a derivative instrument that has been designated as a hedging instrument does not, in and of itself, require dedesignation of that hedging relationship provided that all other hedge accounting criteria continue to be met. Management determined that the adoption of this guidance did not have a material impact on the Consolidated Financial Statements. On January 1, 2017, Arconic adopted changes issued by the FASB to the accounting for Intra-Entity transactions, other than inventory. Previously, no immediate tax impact was recognized in the consolidated financial statements as a result of intra-entity transfers of assets. The previous standard precluded an entity from reflecting a tax benefit or expense from an intra-entity transfer between entities that file separate tax returns, whether or not such entities were in different tax jurisdictions, until the asset was sold to a third party or otherwise recovered. The previous standard also prohibited recognition by the buyer of a deferred tax asset for the temporary difference arising from the excess of the buyer’s tax basis over the cost to the seller. The changes require the current and deferred income tax consequences of the intra-entity transfer to be recorded when the transaction occurs. The exception to defer the tax consequences of inventory transactions is maintained. Management determined that the adoption of this guidance did not have a material impact on the Consolidated Financial Statements. On January 1, 2017, Arconic adopted changes issued by the FASB to the subsequent measurement of goodwill by eliminating step 2 from the goodwill impairment test, which previously required measurement of any goodwill impairment loss by comparing the implied fair value of a reporting unit’s goodwill with the carrying amount of that goodwill. An entity will perform its annual, or interim, goodwill impairment test by comparing the fair value of a reporting unit with its carrying amount and recognize an impairment charge for the amount by which the carrying amount exceeds the reporting unit’s fair value without exceeding the total amount of goodwill allocated to that reporting unit. Arconic applied this new guidance on a prospective basis. See Goodwill policy above for further details. On January 1, 2017, Arconic adopted changes issued by the FASB which narrow the definition of a business and require an entity to evaluate if substantially all of the fair value of the gross assets acquired is concentrated in a single identifiable asset or a group of similar identifiable assets, which would not constitute the acquisition of a business. The guidance also requires a business to include at least one substantive process and narrows the definition of outputs. Arconic applied this new guidance on a prospective basis. Management determined that the adoption of this guidance had no impact on the Consolidated Financial Statements. On January 1, 2017, Arconic adopted changes issued by the FASB to the subsequent measurement of inventory. Previously, an entity was required to measure its inventory at the lower of cost or market, whereby market can be replacement cost, net realizable value, or net realizable value less an approximately normal profit margin. The changes required that inventory be measured at the lower of cost and net realizable value, thereby eliminating the use of the other two market methodologies. Net realizable value is defined as the estimated selling prices in the ordinary course of business less reasonably predictable costs of completion, disposal, and transportation. These changes did not apply to inventories measured using LIFO (last-in, first-out) or the retail inventory method. Arconic applies the net realizable value market option to measure non-LIFO inventories at the lower of cost or market. Management determined that the adoption of this guidance did not have a material impact on the Consolidated Financial Statements. Recently Issued Accounting Guidance. In May 2014, the FASB issued changes to the recognition of revenue from contracts with customers. These changes created a comprehensive framework for all entities in all industries to apply in the determination of when to recognize revenue and, therefore, supersede virtually all existing revenue recognition requirements and guidance. This framework is expected to result in less complex guidance in application while providing a consistent and comparable methodology for revenue recognition. The core principle of the guidance is that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. To achieve this principle, an entity should apply the following steps: (i) identify the contract(s) with a customer, (ii) identify the performance obligations in the contract(s), (iii) determine the transaction price, (iv) allocate the transaction price to the performance obligations in the contract(s), and (v) recognize revenue when, or as, the entity satisfies a performance obligation. In August 2015, the FASB deferred the effective date of the new guidance by one year, making these changes effective for Arconic on January 1, 2018. Arconic will adopt the new guidance using the modified retrospective transition approach, reflecting the cumulative effect of initially applying the new standard to revenue recognition in the first qua

Accumulated Other Comprehensive

Accumulated Other Comprehensive Loss	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Accumulated Other Comprehensive Loss	Accumulated Other Comprehensive Loss The following table details the activity of the four components that comprise Accumulated other comprehensive loss for both Arconic’s shareholders and noncontrolling interests: Arconic Noncontrolling Interests 2017 2016 2015 2017 2016 2015 Pension and other postretirement benefits (U) Balance at beginning of period $ (2,010 ) $ (3,611 ) $ (3,601 ) $ — $ (56 ) $ (64 ) Other comprehensive (loss) income: Unrecognized net actuarial loss and prior service cost/benefit (466 ) (1,112 ) (478 ) — (9 ) 5 Tax benefit (expense) 102 380 170 — 3 (1 ) Total Other comprehensive (loss) income before reclassifications, net of tax (364 ) (732 ) (308 ) — (6 ) 4 Amortization of net actuarial loss and prior service cost/benefit (1) 222 389 458 — 4 6 Tax expense (2) (78 ) (136 ) (160 ) — (1 ) (2 ) Total amount reclassified from Accumulated other comprehensive loss, net of tax (8) 144 253 298 — 3 4 Total Other comprehensive (loss) income (220 ) (479 ) (10 ) — (3 ) 8 Transfer to Alcoa Corporation — 2,080 — — 59 — Balance at end of period $ (2,230 ) $ (2,010 ) $ (3,611 ) $ — $ — $ (56 ) Foreign currency translation Balance at beginning of period $ (689 ) $ (2,412 ) $ (846 ) $ (2 ) $ (780 ) $ (351 ) Other comprehensive income (loss) (3) 252 268 (1,566 ) 2 182 (429 ) Transfer to Alcoa Corporation — 1,455 — — 596 — Balance at end of period $ (437 ) $ (689 ) $ (2,412 ) $ — $ (2 ) $ (780 ) Available-for-sale securities Balance at beginning of period $ 132 $ (5 ) $ — $ — $ — $ — Other comprehensive (loss) income (4) (134 ) 137 (5 ) — — — Transfer to Alcoa Corporation — — — — — — Balance at end of period $ (2 ) $ 132 $ (5 ) $ — $ — $ — Cash flow hedges Balance at beginning of period $ (1 ) $ 597 $ (230 ) — $ (3 ) $ (2 ) Other comprehensive income (loss): Net change from periodic revaluations 37 (843 ) 1,138 — 36 (1 ) Tax (expense) benefit (9 ) 252 (340 ) — (10 ) — Total Other comprehensive income (loss) before reclassifications, net of tax 28 (591 ) 798 — 26 (1 ) Net amount reclassified to earnings: Aluminum contracts (5) (2 ) 1 21 — — — Energy contracts (6) — (49 ) 6 — (34 ) — Foreign exchange contracts (5) — — 5 — — — Interest rate contracts (7) — 9 1 — 5 — Nickel contracts (6) (1 ) 1 2 — — — Sub-total (3 ) (38 ) 35 — (29 ) — Tax benefit (expense) (2) 1 12 (6 ) — 8 — Total amount reclassified from Accumulated other comprehensive loss, net of tax (8) (2 ) (26 ) 29 — (21 ) — Total Other comprehensive income (loss) 26 (617 ) 827 — 5 (1 ) Transfer to Alcoa Corporation — 19 — — (2 ) — Balance at end of period $ 25 $ (1 ) $ 597 $ — $ — $ (3 ) (1) These amounts were included in the computation of net periodic benefit cost for pension and other postretirement benefits (see Note T). (2) These amounts were included in Provision for income taxes on the accompanying Statement of Consolidated Operations. (3) In all periods presented, there were no tax impacts related to rate changes and no amounts were reclassified to earnings. (4) Realized gains and losses were included in Other income, net on the accompanying Statement of Consolidated Operations. (5) These amounts were included in Sales on the accompanying Statement of Consolidated Operations. (6) These amounts were included in Cost of goods sold on the accompanying Statement of Consolidated Operations. (7) These amounts were included in Interest expense on the accompanying Statement of Consolidated Operations. (8) A positive amount indicates a corresponding charge to earnings and a negative amount indicates a corresponding benefit to earnings. These amounts were reflected on the accompanying Statement of Consolidated Operations in the line items indicated in footnotes 1 through 7.

Separation Transaction and Disc

Separation Transaction and Discontinued Operations	12 Months Ended
	Dec. 31, 2017
Discontinued Operations and Disposal Groups [Abstract]
Separation Transaction and Discontinued Operations	Separation Transaction and Discontinued Operations On November 1, 2016, Arconic completed the Separation Transaction. Alcoa Inc., which was re-named Arconic Inc., continues to own the Global Rolled Products (except for the Warrick, IN rolling operations and the equity interest in the rolling mill at the joint venture in Saudi Arabia), Engineered Products and Solutions, and Transportation and Construction Solutions segments. Alcoa Corporation includes the Alumina and Primary Metals segments and the aforementioned Warrick, IN rolling operations and equity interest in the rolling mill at the joint venture in Saudi Arabia, both of which were formally part of the Global Rolled Products segment. Arconic completed the Separation Transaction by distribution on November 1, 2016 of 80.1% of the outstanding common stock of Alcoa Corporation to the Company’s shareholders of record (the “Distribution”) as of the close of business on October 20, 2016 (the “Record Date”). Arconic retained 19.9% of the Alcoa Corporation common stock ( 36,311,767 shares). In the Distribution, each Company shareholder received one share of Alcoa Corporation common stock for every three shares of Arconic common stock held as of the close of business on the Record Date. Shareholders received cash in lieu of fractional shares of Alcoa Corporation common stock. The Company had recorded the retained interest as a cost method investment in Investment in common stock of Alcoa Corporation in the December 2016 Consolidated Balance Sheet. The fair value of Arconic’s retained interest in Alcoa Corporation was $1,020 at December 31, 2016 and was based on the closing stock price of Alcoa Corporation as of December 31, 2016 multiplied by the number of shares of Alcoa Corporation common stock owned by the Company at that date. In February 2017, Arconic sold 23,353,000 of its shares of Alcoa Corporation common stock at $38.03 per share, which resulted in cash proceeds of $888 which were recorded in Sales of investments within Investing Activities in the accompanying Statement of Consolidated Cash Flows, and a gain of $351 which was recorded in Other income, net in the accompanying Statement of Consolidated Operations. In April and May 2017, the Company acquired a portion of its outstanding notes held by two investment banks (the “Investment Banks”) in exchange for cash and the Company’s remaining 12,958,767 Alcoa Corporation shares (valued at $35.91 per share) (the “Debt-for-Equity Exchange”) (See Note I). A gain of $167 on the Debt-for-Equity Exchange was recorded in Other income, net in the accompanying Statement of Consolidated Operations. As of May 4, 2017, the Company no longer maintained a retained interest in Alcoa Corporation common stock. On October 31, 2016, Arconic entered into several agreements with Alcoa Corporation that govern the relationship of the parties following the completion of the Separation Transaction. These agreements include the following: Separation and Distribution Agreement, Transition Services Agreement, Tax Matters Agreement, Employee Matters Agreement, Alcoa Corporation to Arconic Inc. Patent, Know-How, and Trade Secret License Agreement, Arconic Inc. to Alcoa Corporation Patent, Know-How, and Trade Secret License Agreement, Alcoa Corporation to Arconic Inc. Trademark License Agreement, Toll Processing and Services Agreement (the “Toll Processing Agreement”), Master Agreement for the Supply of Primary Aluminum, Massena Lease and Operations Agreement, Fusina Lease and Operations Agreement, and Stockholder and Registration Rights Agreement. Effective November 1, 2016, Arconic entered into a Toll Processing Agreement with Alcoa Corporation for the tolling of metal for the Warrick, IN rolling mill which became a part of Alcoa Corporation upon completion of the Separation Transaction. As part of this arrangement, Arconic provides a toll processing service to Alcoa Corporation to produce can sheet products at its facility in Tennessee through the expected end date of the contract, December 31, 2018. Alcoa Corporation supplies all required raw materials to Arconic and Arconic processes the raw materials into finished can sheet coils ready for shipment to the end customer. Tolling revenues for 2017 and the two-month period ended December 31, 2016 and accounts receivable at December 31, 2017 and December 31, 2016 were not material to the consolidated results of operations and financial position for the years ended December 31, 2017 and December 31, 2016. As part of the Separation Transaction, Arconic was required to provide maximum potential future payment guarantees for Alcoa Corporation issued on behalf of a third party, guarantees related to two long-term Alcoa Corporation energy supply agreements, guarantees related to certain Alcoa Corporation environmental liabilities and energy supply contracts, letters of credit and surety bonds related to Alcoa Corporation workers’ compensation claims which occurred prior to November 1, 2016, and letters of credit for certain Alcoa Corporation equipment leases and energy contracts (see Note K). As part of the Separation Transaction, Arconic had recorded a receivable in the December 2016 Consolidated Balance Sheet for the net after-tax proceeds from Alcoa Corporation’s sale of the Yadkin Hydroelectric Project. The transaction closed and the Company received proceeds of $238 in the first quarter of 2017 and the remaining $5 in the second quarter of 2017. The $243 proceeds were included in Other within Investing Activities in the Statement of Consolidated Cash Flows. The results of operations of Alcoa Corporation were presented as discontinued operations in the Statement of Consolidated Operations as summarized below: Ten months ended October 31, Year ended December 31, 2016 2015 Sales $ 6,752 $ 10,121 Cost of goods sold (exclusive of expenses below) 5,655 7,965 Selling, general administrative, and other expenses 164 214 Research and development 28 69 Provision for depreciation, depletion and amortization 593 772 Restructuring and other charges 102 981 Interest expense 28 25 Other (income) expenses, net (75 ) 30 Income from discontinued operations before income taxes 257 65 Provision for income taxes 73 106 Income (loss) from discontinued operations after income taxes 184 (41 ) Less: Net income from discontinued operations attributable to noncontrolling interests 63 124 Net income (loss) from discontinued operations $ 121 $ (165 ) During 2017, 2016 and 2015, Arconic recognized $18 ( $12 after-tax), $193 ( $158 after-tax) and $24 ( $24 after-tax), respectively, in Selling, general administrative, and other expenses on the accompanying Statement of Consolidated Operations for costs related to the Separation Transaction. In addition, Arconic also incurred capital expenditures and debt issuance costs of $110 during 2016 related to the Separation Transaction. None of the aforementioned costs and expenses related to the Separation Transaction were reclassified into discontinued operations. On November 1, 2016, management evaluated the net assets of Alcoa Corporation for potential impairment and determined that no impairment charge was required. The cash flows related to Alcoa Corporation have not been segregated and are included in the Statement of Consolidated Cash Flows for 2016 and all prior periods presented. The following table presents depreciation, depletion and amortization, restructuring and other charges, and purchases of property, plant and equipment of the discontinued operations related to Alcoa Corporation: For the year ended December 31, 2016 2015 Depreciation, depletion and amortization $ 593 $ 772 Restructuring and other charges $ 102 $ 981 Capital expenditures $ 298 $ 391

Restructuring and Other Charges

Restructuring and Other Charges	12 Months Ended
	Dec. 31, 2017
Restructuring and Related Activities [Abstract]
Restructuring and Other Charges	Restructuring and Other Charges Restructuring and other charges for each year in the three-year period ended December 31, 2017 were comprised of the following: 2017 2016 2015 Asset impairments $ 58 $ 80 $ — Layoff costs 64 70 97 Net loss on divestitures of businesses (F) 57 3 136 Other (3 ) 27 (11 ) Reversals of previously recorded layoff costs (11 ) (25 ) (8 ) Restructuring and other charges $ 165 $ 155 $ 214 Layoff costs were recorded based on approved detailed action plans submitted by the operating locations that specified positions to be eliminated, benefits to be paid under existing severance plans, union contracts or statutory requirements, and the expected timetable for completion of the plans. 2017 Actions . In 2017, Arconic recorded Restructuring and other charges of $165 ( $143 after-tax), which were comprised of the following components: $69 ( $47 after-tax) for layoff costs related to cost reduction initiatives including the separation of approximately 880 employees ( 400 in the Engineered Products and Solutions segment, 245 in the Global Rolled Products segment, 135 in the Transportation and Construction Solutions segment and 100 in Corporate), a charge of $60 ( $60 after-tax) related to the sale of the Fusina, Italy rolling mill; a charge of $41 ( $41 after-tax) for the impairment of assets associated with the agreement to sell the Latin America Extrusions business (see Note F); a net benefit of $6 ( $4 after-tax), for the reversal of forfeited executive stock compensation of $13 , partially offset by a charge of $7 for the related severance; a net charge of $12 ( $7 after-tax) for other miscellaneous items; and a favorable benefit of $11 ( $8 after-tax) for the reversal of a number of small layoff reserves related to prior periods. As of December 31, 2017 , approximately 300 of the 880 employees were separated. The remaining separations for 2017 restructuring programs are expected to be completed by the end of 2018 . In 2017 , cash payments of $28 were made against layoff reserves related to 2017 restructuring programs. 2016 Actions. In 2016, Arconic recorded Restructuring and other charges of $155 ( $114 after-tax), which were comprised of the following components: $57 ( $46 after-tax) for costs related to the exit of certain legacy Firth Rixson operations in the U.K.; $37 ( $24 after-tax) for exit costs related to the decision to permanently shut down a can sheet facility; $20 ( $14 after-tax) for costs related to the closures of five facilities, primarily in the Transportation and Construction Solutions segment and Engineered Products and Solutions segment, including the separation of approximately 280 employees; $53 ( $33 after-tax) for other layoff costs, including the separation of approximately 1,315 employees ( 1,045 in the Engineered Products and Solutions segment, 210 in Corporate, 30 in the Global Rolled Products segment and 30 in the Transportation and Construction Solutions segment); $11 ( $8 after-tax) for other miscellaneous items, including $3 ( $2 after-tax) for the sale of Remmele Medical; $2 ( $1 after-tax) for a pension settlement; and $25 ( $12 after-tax) for the reversal of a number of small layoff reserves related to prior periods. In 2016, management made the decision to exit certain legacy Firth Rixson facilities in the U.K. Costs related to these actions included asset impairments and accelerated depreciation of $51 ; other exit costs of $4 ; and $2 for the separation of 60 employees. Also in 2016, management approved the shutdown and demolition of the can sheet facility in Tennessee upon completion of the Toll Processing Agreement with Alcoa Corporation. Costs related to this action included $21 in asset impairments; $9 in other exit costs; and $7 for the separation of 145 employees. The other exit costs of $9 represent $4 in asset retirement obligations and $3 in environmental remediation, both of which were triggered by the decision to permanently shut down and demolish the can sheet facility in Tennessee, and $2 in other exit costs. As of December 31, 2017 , approximately 1,280 of the 1,700 (previously 1,750 ) employees were separated. The total number of employees associated with 2016 restructuring programs was updated to reflect employees, who were initially identified for separation, accepting other positions within Arconic and natural attrition. The remaining separations for 2016 restructuring programs are expected to be completed by the end of 2018. In 2017 and 2016, cash payments of $26 and $16 were made against layoff reserves related to 2016 restructuring programs. 2015 Actions. In 2015, Arconic recorded Restructuring and other charges of $214 ( $192 after-tax), which were comprised of the following components: a $136 ( $134 after-tax) net loss related to the March 2015 divestiture of a rolling mill in Russia and post-closing adjustments associated with the December 2014 divestitures of three rolling mills located in Spain and France; $97 ( $70 after-tax) for layoff costs, including the separation of approximately 1,505 employees ( 590 in the Engineered Products and Solutions segment, 425 in the Transportation and Construction Solutions segment, 400 in Corporate and 90 in the Global Rolled Products segment); an $18 ( $13 after-tax) gain on the sale of land related to one of the rolling mills in Australia that was permanently closed in December 2014; a net charge of $7 ( $4 after-tax) for other miscellaneous items; and $8 ( $3 after-tax) for the reversal of a number of small layoff reserves related to prior periods. As of December 31, 2017 , the separations associated with the 2015 restructuring programs were essentially complete. In 2017, 2016 and 2015, cash payments of $5 , $55 and $18 , respectively, were made against layoff reserves related to 2015 restructuring programs. Arconic does not include Restructuring and other charges in the results of its reportable segments. The pre-tax impact of allocating such charges to segment results would have been as follows: 2017 2016 2015 Engineered Products and Solutions $ 30 $ 78 $ 46 Global Rolled Products 72 40 121 Transportation and Construction Solutions 52 14 8 Segment total 154 132 175 Corporate 11 23 39 Total restructuring and other charges $ 165 $ 155 $ 214 Activity and reserve balances for restructuring charges were as follows: Layoff costs Other exit costs Total Reserve balances at December 31, 2014 $ 48 $ 20 $ 68 2015: Cash payments (45 ) (12 ) (57 ) Restructuring charges 97 7 104 Other* (16 ) (6 ) (22 ) Reserve balances at December 31, 2015 84 9 93 2016: Cash payments (73 ) (13 ) (86 ) Restructuring charges 70 27 97 Other* (31 ) (14 ) (45 ) Reserve balances at December 31, 2016 50 9 59 2017: Cash payments (59 ) (6 ) (65 ) Restructuring charges 64 1 65 Other* 1 (2 ) (1 ) Reserve balances at December 31, 2017 $ 56 $ 2 $ 58 * Other includes reversals of previously recorded restructuring charges and the effects of foreign currency translation. In 2017, Other for layoff costs also includes the reclassification of a stock awards reversal of $13 . In 2016, Other for other exit costs also included a reclassification of $8 in asset retirement and $2 in environmental obligations, as these liabilities were included in Arconic’s separate reserves for asset retirement obligations and environmental remediation. Other for other exit costs also included a reclassification of $4 in legal obligations, as these liabilities were included in Arconic’s separate reserves for legal costs. In 2015, Other for other exit costs included a reclassification of $5 for certain obligations included in Arconic’s separate reserves for warranties, lease terminations and tax indemnities. The remaining reserves are expected to be paid in cash during 2018.

Goodwill and Other Intangible A

Goodwill and Other Intangible Assets	12 Months Ended
	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Other Intangible Assets	Goodwill and Other Intangible Assets The following table details the changes in the carrying amount of goodwill: Engineered Global Rolled Products Transportation and Construction Solutions Corporate* Total Balances at December 31, 2015 Goodwill $ 4,660 $ 201 $ 111 $ 330 $ 5,302 Accumulated impairment losses — — (53 ) — (53 ) 4,660 201 58 330 5,249 Acquisitions and Divestitures (F) 47 — — — 47 Translation and other (128 ) (20 ) (1 ) 1 (148 ) Balances at December 31, 2016 Goodwill 4,579 181 110 331 5,201 Accumulated impairment losses — — (53 ) — (53 ) 4,579 181 57 331 5,148 Impairment (A) (719 ) — — — (719 ) Translation and other 89 12 3 2 106 Balances at December 31, 2017 Goodwill 4,668 193 113 333 5,307 Accumulated impairment losses (719 ) — (53 ) — (772 ) $ 3,949 $ 193 $ 60 $ 333 $ 4,535 * As of December 31, 2017 , the amount reflected in Corporate is allocated to Arconic’s three reportable segments ( $256 to Engineered Products and Solutions, $59 to Global Rolled Products and $18 to Transportation and Construction Solutions) for purposes of impairment testing (see Goodwill policy in Note A). This goodwill is reflected in Corporate for segment reporting purposes because it is not included in management’s assessment of performance by the three reportable segments. In 2017, Arconic recognized an impairment of goodwill in the amount of $719 related to the annual impairment review of the AFE reporting unit which is included in the Engineered Products and Solutions segment. In 2015, Arconic recognized an impairment of goodwill in the amount of $25 related to the annual impairment review of the soft alloy extrusion business reporting unit which is included in the Transportation and Construction Solutions segment (see Goodwill policy in Note A). Other intangible assets were as follows: December 31, 2017 Gross carrying amount Accumulated amortization Computer software $ 789 $ (674 ) Patents and licenses 110 (107 ) Other intangibles 953 (116 ) Total amortizable intangible assets 1,852 (897 ) Indefinite-lived trade names and trademarks 32 — Total other intangible assets $ 1,884 $ (897 ) December 31, 2016 Gross carrying amount Accumulated amortization Computer software $ 755 $ (623 ) Patents and licenses 110 (102 ) Other intangibles 897 (81 ) Total amortizable intangible assets 1,762 (806 ) Indefinite-lived trade names and trademarks 32 — Total other intangible assets $ 1,794 $ (806 ) Computer software consists primarily of software costs associated with an enterprise business solution (EBS) within Arconic to drive common systems among all businesses. Amortization expense related to the intangible assets in the tables above for the years ended December 31, 2017 , 2016 , and 2015 was $71 , $65 , and $67 , respectively, and is expected to be in the range of approximately $60 to $75 annually from 2018 to 2022.

Acquisitions and Divestitures

Acquisitions and Divestitures	12 Months Ended
	Dec. 31, 2017
Business Combinations [Abstract]
Acquisitions and Divestitures	Acquisitions and Divestitures Pro forma results of the Company, assuming all acquisitions described below were made at the beginning of the earliest prior period presented, would not have been materially different from the results reported. 2017 Divestitures . In March 2017, Arconic completed the sale of its Fusina, Italy rolling mill to Slim Aluminium. While owned by Arconic, the operating results and assets and liabilities of the Fusina, Italy rolling mill were included in the Global Rolled Products segment. As part of the transaction, Arconic injected $10 of cash into the business and provided a third-party guarantee with a fair value of $5 related to Slim Aluminium’s environmental remediation. The Company recorded a loss on the sale of $60 , which was recorded in Restructuring and other charges (see Note D) on the Statement of Consolidated Operations for 2017. The rolling mill generated third-party sales of approximately $54 and $165 for 2017 and 2016, respectively. At the time of the divestiture, the rolling mill had approximately 312 employees. In December 2017, Arconic entered into an agreement to sell its Latin America Extrusions business for $10 million in cash, subject to working capital and other adjustments. The Latin America Extrusions business operates primarily in Brazil and is part of the Company’s Transportation and Construction Solutions segment. Following customary regulatory and anti-trust approvals, the ownership of this business is expected to be transferred to a subsidiary of Hydro Extruded Solutions AS in the first half of 2018. As a result of the transaction, Arconic recognized a charge of $41 million in the fourth quarter of 2017 primarily related to the non-cash impairment of the net book value of the business (See Notes A and D). 2016 Divestitures . In April 2016, Arconic completed the sale of the Remmele Medical business to LISI MEDICAL for $102 in cash ( $99 net of transaction costs), which was included in Proceeds from the sale of assets and businesses on the accompanying Statement of Consolidated Cash Flows. This business, which was part of the RTI International Metals Inc. (RTI) acquisition (see below), manufactured precision-machined metal products for customers in the minimally invasive surgical device and implantable device markets. Since this transaction occurred within a year of the completion of the RTI acquisition, no gain was recorded on this transaction as the excess of the proceeds over the carrying value of the net assets of this business was reflected as a purchase price adjustment (decrease to goodwill of $44 ) to the final allocation of the purchase price related to Arconic’s acquisition of RTI. While owned by Arconic, the operating results and assets and liabilities of this business were included in the Engineered Products and Solutions segment. This business generated sales of approximately $20 from January 1, 2016 through the divestiture date, April 29, 2016, and, at the time of the divestiture, had approximately 330 employees. 2015 Acquisitions . In March 2015, Arconic completed the acquisition of an aerospace structural castings company, TITAL, for $204 ( €188 ) in cash (an additional $1 ( €1 ) was paid in September 2015 to settle working capital in accordance with the purchase agreement). TITAL, a privately held company with approximately 650 employees at the time of the acquisition and based in Germany, produces aluminum and titanium investment casting products for the aerospace and defense markets. The purpose of this acquisition was to capture increasing demand for advanced jet engine components made of titanium, establish titanium-casting capabilities in Europe, and expand existing aluminum casting capacity. The assets, including the associated goodwill, and liabilities of this business were included within Arconic’s Engineered Products and Solutions segment since the date of acquisition. Based on the preliminary allocation of the purchase price, goodwill of $118 was recorded for this transaction. In the first quarter of 2016, the allocation of the purchase price was finalized, based, in part, on the completion of a third-party valuation of certain assets acquired, resulting in a $1 reduction of the initial goodwill amount. None of the $117 in goodwill is deductible for income tax purposes and no other intangible assets were identified. In July 2015, Arconic completed the acquisition of RTI, a U.S. company that was publicly traded on the New York Stock Exchange under the ticker symbol “RTI.” Arconic purchased all outstanding shares of RTI common stock in a stock-for-stock transaction valued at $870 (based on the $9.96 per share July 23, 2015 closing price of Arconic’s common stock). Each issued and outstanding share of RTI common stock prior to the completion of the transaction was converted into the right to receive 2.8315 shares of Arconic common stock. In total, Arconic issued 29,132,471 shares ( 87,397,414 shares pre-reverse stock split – see Note O) of its common stock to consummate this transaction, which was not reflected in the accompanying Statement of Consolidated Cash Flows as it represents a noncash financing activity. The exchange ratio was the quotient of a $41 per RTI common share acquisition price and the $14.48 per share March 6, 2015 closing price of Arconic’s common stock. In addition to the transaction price, Arconic also paid $25 ( $19 after-tax) in professional fees and costs related to this acquisition. This amount was recorded in Selling, general administrative, and other expenses on the accompanying Statement of Consolidated Operations. RTI is a global supplier of titanium and specialty metal products and services for the commercial aerospace, defense, energy, and medical device end markets. The purpose of this acquisition was to expand Arconic’s range of titanium offerings and add advanced technologies and materials, primarily related to the aerospace end market. In 2014, RTI generated net sales of $794 and had approximately 2,600 employees. The operating results and assets and liabilities of RTI were included within Arconic’s Engineered Products and Solutions segment since the date of acquisition. Third-party sales and Adjusted EBITDA (Arconic’s primary segment performance measure – see Note N) of RTI from the acquisition date through December 31, 2015 were $309 and $21 , respectively. During the third quarter of 2016, the final purchase price allocation was completed. Arconic recognized goodwill of $298 , which represents the earnings growth potential of RTI, Arconic’s ability to expand its titanium capabilities in the aerospace market, and expected synergies from combining the operations of the two companies. This goodwill was allocated to a new Arconic reporting unit associated with the Engineered Products and Solutions segment, ATEP, which consists solely of the acquired RTI business. None of this goodwill is deductible for income tax purposes. Arconic also recorded intangible assets of $37 consisting mainly of customer relationships which are being amortized over a period of 20 years. As part of this acquisition, Arconic assumed the obligation to repay two tranches of convertible debt; one tranche was due and settled in cash on December 1, 2015 (principal amount of $115 ) and the other tranche is due on October 15, 2019 (principal amount of $403 ), unless earlier converted or purchased by Arconic at the holder’s option under specific conditions. Upon conversion of the 2019 convertible notes, holders will receive, at Arconic’s election, cash, shares of common stock (approximately 14,294,000 shares using the December 31, 2017 conversion rate of 35.5119 shares per $1,000 (not in millions) bond or per-share conversion price of $28.1596 ), or a combination of cash and shares. On the maturity date, each holder of outstanding notes will be entitled to receive $1,000 (not in millions) in cash for each $1,000 (not in millions) bond, together with accrued and unpaid interest. The cash conversion feature requires the convertible notes to be bifurcated into a liability component and an equity component. The fair value of the liability component was determined by calculating the net present value of the cash flows of the convertible notes using the interest rate of a similar instrument without a conversion feature. The fair value of the equity component is the difference between the fair value of the entire instrument on the date of acquisition and the fair value of the liability and is included as Additional capital on the accompanying Consolidated Balance Sheet. 2015 Divestitures. In 2015, Arconic completed the divestiture of an operation in Russia (see below) and had post-closing adjustments, as provided for in the respective purchase agreements, related to a divestiture completed in December 2014. The divestiture and post-closing adjustments combined resulted in net cash paid of $11 and a net loss of $137 , which was recorded in Restructuring and other charges (see Note D) on the accompanying Statement of Consolidated Operations. In March 2015, Arconic completed the sale of a rolling mill located in Belaya Kalitva, Russia to a wholly-owned subsidiary of Stupino Titanium Company. While owned by Arconic, the operating results and assets and liabilities of the rolling mill were included in the Global Rolled Products segment. The rolling mill generated sales of approximately $130 in 2014 and, at the time of divestiture, had approximately 1,870 employees. 2014 Acquisitions. In November 2014, Arconic acquired Firth Rixson. The purchase price included an earn-out agreement that required Arconic to make earn-out payments up to an aggregate maximum amount of $150 through December 31, 2020 upon certain conditions. This earn-out was contingent on the Firth Rixson forging business in Savannah, Georgia achieving certain identified financial targets through December 31, 2020. During the fourth quarter of 2016, management determined that payment of the maximum amount was not probable based on the forecasted financial performance of this location. Therefore, the fair value of this liability was reduced by $56 with a corresponding credit to Other income, net on the accompanying Statement of Consolidated Operations. During the fourth quarter of 2017, management determined that payment of the remaining amount of the contingent liability was not probable based on the forecasted financial performance of this location. Therefore, the fair value of this liability was reduced by $81 to zero at December 31, 2017 with a corresponding credit to Other income, net on the accompanying Statement of Consolidated Operations.

Inventories

Inventories	12 Months Ended
	Dec. 31, 2017
Inventory Disclosure [Abstract]
Inventories	Inventories December 31, 2017 2016 Finished goods $ 669 $ 625 Work-in-process 1,349 1,144 Purchased raw materials 381 408 Operating supplies 81 76 $ 2,480 $ 2,253 At December 31, 2017 and 2016 , the total amount of inventories valued on a LIFO basis was $1,208 and $947 , respectively. If valued on an average-cost basis, total inventories would have been $481 and $371 higher at December 31, 2017 and 2016 , respectively. During 2017 and 2016 , reductions in LIFO inventory quantities caused partial liquidations of the lower cost LIFO inventory base. These liquidations resulted in the recognition of immaterial income amounts in 2017 , 2016 , and 2015 .

Properties, Plants, and Equipme

Properties, Plants, and Equipment, Net	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Properties, Plants, and Equipment, Net	Properties, Plants, and Equipment, Net December 31, 2017 2016 Land and land rights $ 140 $ 135 Structures: Engineered Products and Solutions 784 733 Global Rolled Products 1,090 1,061 Transportation and Construction Solutions 268 254 Other 253 248 2,395 2,296 Machinery and equipment: Engineered Products and Solutions 3,054 2,728 Global Rolled Products 4,641 4,570 Transportation and Construction Solutions 777 723 Other 358 337 8,830 8,358 11,365 10,789 Less: accumulated depreciation and amortization 6,392 6,073 4,973 4,716 Construction work-in-progress 621 783 $ 5,594 $ 5,499

Debt

Debt	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Debt	Debt Long-Term Debt. December 31, 2017 2016 6.50% Bonds, due 2018 $ — $ 250 6.75% Notes, due 2018 — 750 5.72% Notes, due 2019 500 750 1.63% Convertible Notes, due 2019* 403 403 6.150% Notes, due 2020 1,000 1,000 5.40% Notes, due 2021 1,250 1,250 5.87% Notes, due 2022 627 627 5.125% Notes, due 2024 1,250 1,250 5.90% Notes, due 2027 625 625 6.75% Bonds, due 2028 300 300 5.95% Notes due 2037 625 625 Iowa Finance Authority Loan, due 2042 (4.75%) 250 250 Other** (23 ) (32 ) 6,807 8,048 Less: amount due within one year 1 4 $ 6,806 $ 8,044 * Amount was assumed in conjunction with the acquisition of RTI (see Note F). ** Other includes various financing arrangements related to subsidiaries, unamortized debt discounts related to the outstanding notes and bonds listed in the table above, an equity option related to the convertible notes due in 2019 (see Note F), adjustments to the carrying value of long-term debt related to an interest swap contract accounted for as a fair value hedge that was unwound during 2017, and unamortized debt issuance costs. The principal amount of long-term debt maturing in each of the next five years is $1 in 2018 , $903 in 2019 , $1,000 in 2020 , $1,250 in 2021 , and $627 in 2022 . Public Debt —In April 2017, the Company announced three separate cash tender offers by the Investment Banks for the purchase of the Company’s 6.50% Bonds due 2018 (the “6.50% Bonds”), 6.75% Notes due 2018 (the “6.75% Notes”), and 5.72% Notes due 2019 (the “5.72% Notes”), up to a maximum purchase amount of $1,000 aggregate principal amount of notes, subject to certain conditions. The Investment Banks purchased notes totaling $805 aggregate principal amount, including $150 aggregate principal amount of 6.50% Bonds, $405 aggregate principal amount of 6.75% Notes, and $250 aggregate principal amount of $5.72% Notes. During the second quarter of 2017, the Company agreed to acquire the notes from the Investment Banks for $409 in cash plus its remaining investment in Alcoa Corporation common stock ( 12,958,767 shares valued at $35.91 per share) for total consideration of $874 including accrued and unpaid interest. The Company recorded a charge of $58 ( $27 in cash) primarily for the premium for the early redemption of the notes, a benefit of $8 for the proceeds of a related interest rate swap agreement, and a charge of $2 for legal fees associated with the transaction in Interest expense, and recorded a gain of $167 in Other income, net in the accompanying Statement of Consolidated Operations for the Debt-for-Equity Exchange. On June 19, 2017, the Company completed the early redemption of its remaining outstanding 6.50% Bonds, with aggregate principal amount of $100 , and its remaining outstanding 6.75% Notes, with aggregate principal amount of $345 , for $479 in cash including accrued and unpaid interest. As a result of the early redemption of the 6.50% Bonds and 6.75% Notes, the Company recorded a charge of $24 in Interest expense in the accompanying Statement of Consolidated Operations for the premium paid for the early redemption of these notes in excess of their carrying value. In December 2016, Arconic elected to call for redemption the $750 in outstanding principal of its 5.55% Notes due February 2017 (the “2017 Notes”) under the provisions of the 2017 Notes. The total cash paid to the holders of the called 2017 Notes was $770 , which includes $17 in accrued and unpaid interest from the last interest payment date up to, but not including, the settlement date, and a $3 purchase premium. The purchase premium was recorded in Interest expense on the accompanying Statement of Consolidated Operations. This transaction was completed on December 30, 2016. The Company has the option to redeem certain of its Notes and Bonds in whole or part, at any time at a redemption price equal to the greater of principal amount or the sum of the present values of the remaining scheduled payments, discounted using a defined treasury rate plus a spread, plus in either case accrued and unpaid interest to the redemption date. Credit Facilities. On July 25, 2014, Arconic entered into a Five -Year Revolving Credit Agreement (“the Credit Agreement”) with a syndicate of lenders and issuers named therein which provides for a senior unsecured revolving credit facility (the “Credit Facility”). The proceeds are to be used to provide working capital or for other general corporate purposes of Arconic. By an Extension Request and Amendment Letter dated as of June 5, 2015, the maturity date of the Credit Facility was extended to July 25, 2020. In September 2016, Arconic entered into an amendment to the Credit Agreement to permit the Separation Transaction and to amend certain terms of the Credit Agreement including the replacement of the existing financial covenant with a leverage ratio and reduction of total commitments available from $4,000 to $3,000 . The amendment became effective on the separation date of November 1, 2016. The previous financial covenant, based upon Consolidated Net Worth (as defined in the Credit Agreement) was replaced. Arconic is required to maintain a ratio of Indebtedness (as defined in the Credit Agreement), to Consolidated EBITDA (as defined in the Credit Agreement) of 4.50 to 1.00 for the period of the four fiscal quarters most recently ended, declining to 3.50 to 1.00 on December 31, 2019 and thereafter. The Credit Agreement includes additional covenants, including, among others, (a) limitations on Arconic’s ability to incur liens securing indebtedness for borrowed money, (b) limitations on Arconic’s ability to consummate a merger, consolidation or sale of all or substantially all of its assets, and (c) limitations on Arconic’s ability to change the nature of its business. As of December 31, 2017, Arconic was in compliance with all such covenants. The Credit Facility matures on July 25, 2020 , unless extended or earlier terminated in accordance with the provisions of the Credit Agreement. Arconic may make one additional one -year extension request during the remaining term of the Credit Facility, subject to the lender consent requirements set forth in the Credit Agreement. Under the provisions of the Credit Agreement, Arconic will pay a fee up to 0.30% (based on Arconic’s long-term debt ratings as of December 31, 2017 ) of the total commitment per annum to maintain the Credit Facility. The Credit Facility is unsecured and amounts payable under it will rank pari passu with all other unsecured, unsubordinated indebtedness of Arconic. Borrowings under the Credit Facility may be denominated in U.S. dollars or euros. Loans will bear interest at a base rate or a rate equal to LIBOR, plus, in each case, an applicable margin based on the credit ratings of Arconic’s outstanding senior unsecured long-term debt. The applicable margin on base rate loans and LIBOR loans will be 0.70% and 1.70% per annum, respectively, based on Arconic’s long-term debt ratings as of December 31, 2017 . Loans may be prepaid without premium or penalty, subject to customary breakage costs. The obligation of Arconic to pay amounts outstanding under the Credit Facility may be accelerated upon the occurrence of an “Event of Default” as defined in the Credit Agreement. Such Events of Default include, among others, (a) Arconic’s failure to pay the principal of, or interest on, borrowings under the Credit Facility, (b) any representation or warranty of Arconic in the Credit Agreement proving to be materially false or misleading, (c) Arconic’s breach of any of its covenants contained in the Credit Agreement, and (d) the bankruptcy or insolvency of Arconic. There were no amounts outstanding at December 31, 2017 and 2016 and no amounts were borrowed during 2017 , 2016 or 2015 under the Credit Facility. In addition to the Credit Facility above, Arconic has a number of other credit facilities that provide a combined borrowing capacity of $715 as of December 31, 2017 , of which $640 is due to expire in 2018 and $75 is due to expire in 2019 . The purpose of any borrowings under these credit arrangements is to provide for working capital requirements and for other general corporate purposes. The covenants contained in all these arrangements are the same as the Credit Agreement (see above). In 2017 , 2016 and 2015 , Arconic borrowed and repaid $810 , $1,950 , and $1,890 , respectively, under the respective credit arrangements. The weighted-average interest rate and weighted-average days outstanding of the respective borrowings during 2017 , 2016 and 2015 were 2.6% , 1.9% , and 1.6% , respectively, and 46 days, 49 days, and 69 days, respectively. Short-Term Debt. At December 31, 2017 and 2016 , short-term debt was $38 and $40 , respectively. These amounts included $33 and $31 at December 31, 2017 and 2016 , respectively, related to accounts payable settlement arrangements with certain vendors and third-party intermediaries. These arrangements provide that, at the vendor’s request, the third-party intermediary advances the amount of the scheduled payment to the vendor, less an appropriate discount, before the scheduled payment date and Arconic makes payment to the third-party intermediary on the date stipulated in accordance with the commercial terms negotiated with its vendors. Arconic records imputed interest related to these arrangements in Interest expense on the accompanying Statement of Consolidated Operations. Commercial Paper. Arconic had no outstanding commercial paper at December 31, 2017 and 2016 . In 2017 and 2016 , the average outstanding commercial paper was $67 and $127 , respectively. Commercial paper matures at various times within one year and had an annual weighted average interest rate of 1.6% , 1.1% , and 0.6% during 2017 , 2016 , and 2015 , respectively.

Other Noncurrent Liabilities an

Other Noncurrent Liabilities and Deferred Credits	12 Months Ended
	Dec. 31, 2017
Payables and Accruals [Abstract]
Other Noncurrent Liabilities and Deferred Credits	Other Noncurrent Liabilities and Deferred Credits December 31, 2017 2016 Environmental remediation (L) $ 253 $ 260 Income taxes (Q) 162 154 Accrued compensation and retirement costs 218 216 Contingent payment related to an acquisition (F) — 78 Other 126 162 $ 759 $ 870

Contingencies and Commitments

Contingencies and Commitments	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Contingencies and Commitments	Contingencies and Commitments Contingencies Environmental Matters. Arconic participates in environmental assessments and cleanups at more than 100 locations. These include owned or operating facilities and adjoining properties, previously owned or operating facilities and adjoining properties, and waste sites, including Superfund (Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) sites. A liability is recorded for environmental remediation when a cleanup program becomes probable and the costs can be reasonably estimated. As assessments and cleanups proceed, the liability is adjusted based on progress made in determining the extent of remedial actions and related costs. The liability can change substantially due to factors such as the nature and extent of contamination, changes in remedial requirements, and technological changes, among others. Arconic’s remediation reserve balance was $294 at December 31, 2017 and $308 at December 31, 2016 (of which $41 and $48 , respectively, was classified as a current liability), and reflects the most probable costs to remediate identified environmental conditions for which costs can be reasonably estimated. In 2017, the remediation reserve increased by $5 due to a net charge associated with a number of sites and was recorded in Costs of goods sold on the accompanying Statement of Consolidated Operations. The change in the reserve also reflects an increase of $8 due to a reclassification of amounts included in other reserves within Other noncurrent liabilities and deferred credits on the accompanying Consolidated Balance Sheet, and a decrease of $1 due to the effects of foreign currency translation. Payments related to remediation expenses applied against the reserve were $26 in 2017 and include expenditures currently mandated, as well as those not required by any regulatory authority or third party. Included in annual operating expenses are the recurring costs of managing hazardous substances and environmental programs. These costs are estimated to be approximately 1% or less of cost of goods sold. The following discussion provides details regarding the current status of the most significant remediation reserve related to a current Arconic site. Massena West, NY— Arconic has an ongoing remediation project related to the Grasse River, which is adjacent to Arconic’s Massena plant site. Many years ago, it was determined that sediments and fish in the river contain varying levels of polychlorinated biphenyls (PCBs). The project, which was selected by the U.S. Environmental Protection Agency (EPA) in a Record of Decision issued in April 2013, is aimed at capping PCB contaminated sediments with concentration in excess of one part per million in the main channel of the river and dredging PCB contaminated sediments in the near-shore areas where total PCBs exceed one part per million. At December 31, 2017 and December 31, 2016 , the reserve balance associated with this matter was $215 and $228 , respectively. Arconic is in the planning and design phase of the project, which phase is now expected to be completed in 2018. Originally, the design was scheduled to be completed and approved by the EPA in 2017, but in the third quarter of 2017, the New York State Department of Environmental Conservation (DEC) sent a letter to EPA requesting revisions to the draft design. That caused EPA to delay their review and comment on the draft design. EPA has now responded to the DEC letter and while issues remain, Arconic is now able to recommence work on the final design. Following submittal of the final design and EPA approval, the actual remediation fieldwork is expected to commence and take approximately four years . The majority of the project funding is expected to be incurred between 2018 and 2022 . Tax. Pursuant to the Tax Matters Agreement (see Note C), dated as of October 31, 2016, entered into between the Company and Alcoa Corporation in connection with the Separation, the Company shares responsibility with Alcoa Corporation for, and Alcoa Corporation has agreed to partially indemnify the Company with respect to the following matter. As previously reported, in September 2010, following a corporate income tax audit covering the 2003 through 2005 tax years, an assessment was received as a result of Spain’s tax authorities disallowing certain interest deductions claimed by a Spanish consolidated tax group owned by the Company. An appeal of this assessment in Spain’s Central Tax Administrative Court by the Company was denied in October 2013. In December 2013, the Company filed an appeal of the assessment in Spain’s National Court. On January 16, 2017, Spain’s National Court issued a decision in favor of the Company related to the assessment received in September 2010. The Spanish Tax Administration did not file an appeal within the applicable period. Based on this decision and recent confirming correspondence from the Spanish Tax Administration, the matter is now closed. The Company will not be responsible for any assessment related to the 2003 through 2005 tax years. Additionally, following a corporate income tax audit of the same Spanish tax group for the 2006 through 2009 tax years, Spain’s tax authorities issued an assessment in July 2013 similarly disallowing certain interest deductions. In August 2013, the Company filed an appeal of this second assessment in Spain’s Central Tax Administrative Court, which was denied in January 2015. The Company filed an appeal of this second assessment in Spain’s National Court in March 2015. Spain’s National Court has not yet rendered a decision related to the assessment received in July 2013. The assessment for the 2006 through 2009 tax years is $155 ( €130 ), including interest. The Company believes it has meritorious arguments to support its tax position and intends to vigorously litigate the assessments through Spain’s court system. However, in the event the Company is unsuccessful, a portion of the assessments may be offset with existing net operating losses available to the Spanish consolidated tax group, which would be shared between the Company and Alcoa Corporation as provided for in the Tax Matters Agreement. Additionally, while the tax years 2010 through 2013 are closed to audit, it is possible that the Company may receive similar assessments for tax years subsequent to 2013. At this time, the Company is unable to reasonably predict an ultimate outcome for this matter. Reynobond PE. As previously reported, on June 13, 2017, the Grenfell Tower in London, UK caught fire resulting in fatalities, injuries and damage. A French subsidiary of Arconic, Arconic Architectural Products SAS (AAP SAS), supplied a product, Reynobond PE, to its customer, a cladding system fabricator, which used the product as one component of the overall cladding system on Grenfell Tower. The fabricator supplied its portion of the cladding system to the façade installer, who then completed and installed the system under the direction of the general contractor. Neither Arconic nor AAP SAS was involved in the design or installation of the system used at the Grenfell Tower, nor did it have a role in any other aspect of the building’s refurbishment or original design. Regulatory investigations into the overall Grenfell Tower matter are being conducted, including a criminal investigation by the London Metro Police, a Public Inquiry by the British government and a consumer protection inquiry by a French public authority. AAP SAS sought and received core participant status in the Public Inquiry. The Company will no longer sell the PE product for architectural use on buildings. In August and September 2017, two purported class action complaints were filed against Arconic and certain officers, directors and/or other parties, alleging that, in light of the Grenfell Tower fire, certain Company filings with the Securities and Exchange Commission contained false and misleading disclosures and omissions in violation of the federal securities laws. Those cases remain pending. While the Company believes that these cases are without merit and intends to challenge them vigorously, there can be no assurances regarding the ultimate resolution of these matters. Given the preliminary nature of these matters and the uncertainty of litigation, the Company cannot reasonably estimate at this time the likelihood of an unfavorable outcome or the possible loss or range of losses in the event of an unfavorable outcome. The Board of Directors has also received letters, purportedly sent on behalf of shareholders, reciting allegations similar to those made in the federal court lawsuits and demanding that the Board authorize the Company to initiate litigation against members of management, the Board and others. The Board of Directors has appointed a Special Litigation Committee to review these shareholder demand letters and is considering the appropriate course of action. In addition, lawsuits are pending in state court in New York and federal court in Pennsylvania, initiated, respectively, by another purported shareholder and by the Company, concerning the shareholder’s claimed right, which the Company contests, to inspect the Company’s books and records related to the Grenfell Tower fire and Reynobond PE. Other. In addition to the matters discussed above, various other lawsuits, claims, and proceedings have been or may be instituted or asserted against Arconic, including those pertaining to environmental, product liability, safety and health, employment, and tax matters. While the amounts claimed in these other matters may be substantial, the ultimate liability cannot currently be determined because of the considerable uncertainties that exist. Therefore, it is possible that the Company’s liquidity or results of operations in a period could be materially affected by one or more of these other matters. However, based on facts currently available, management believes that the disposition of these other matters that are pending or asserted will not have a material adverse effect, individually or in the aggregate, on the results of operations, financial position or cash flows of the Company. Commitments Purchase Obligations. Arconic has entered into purchase commitments for raw materials, energy and other goods and services, which total $861 in 2018 , $176 in 2019 , $74 in 2020 , $13 in 2021 , $6 in 2022 , and $5 thereafter. Operating Leases. Certain land and buildings, plant equipment, vehicles, and computer equipment are under operating lease agreements. Total expense for all leases was $113 in 2017 , $110 in 2016 , and $112 in 2015 . Under long-term operating leases, minimum annual rentals are $108 in 2018 , $88 in 2019 , $62 in 2020 , $46 in 2021 , $38 in 2022 , and $100 thereafter. Guarantees. At December 31, 2017 , Arconic has outstanding bank guarantees related to tax matters, outstanding debt, workers’ compensation, environmental obligations, energy contracts, and customs duties, among others. The total amount committed under these guarantees, which expire at various dates between 2018 and 2026 was $29 at December 31, 2017. Pursuant to the Separation and Distribution Agreement, Arconic was required to provide certain guarantees for Alcoa Corporation, which had a combined fair value of $8 and $35 at December 31, 2017 and 2016, respectively, and were included in Other noncurrent liabilities and deferred credits on the accompanying Consolidated Balance Sheet. Arconic was required to provide payment guarantees for Alcoa Corporation issued on behalf of a third party, and amounts outstanding under these payment guarantees were $197 and $354 at December 31, 2017 and 2016, respectively. These guarantees expire at various times between 2018 and 2024, and relate to project financing for Alcoa Corporation’s aluminum complex in Saudi Arabia. Furthermore, Arconic was required to provide guarantees related to two long-term supply agreements for energy for Alcoa Corporation facilities in the event of an Alcoa Corporation payment default. In October 2017, Alcoa Corporation announced that it had terminated one of the two agreements, the electricity contract with Luminant Generation Company LLC that was tied to its Rockdale Operations, effective as of October 1, 2017. As a result of the termination of the Rockdale electricity contract, Arconic recorded income of $25 in the fourth quarter of 2017 associated with reversing the fair value of the electricity contract guarantee. For the remaining long-term supply agreement, Arconic is required to provide a guarantee up to an estimated present value amount of approximately $1,297 . Arconic was also required to provide guarantees of $50 related to two Alcoa Corporation energy supply contracts. These guarantees expired in March 2017. Additionally, Arconic was required to provide guarantees of $53 related to certain Alcoa Corporation environmental liabilities. Notification of a change in guarantor to Alcoa Corporation was made to the appropriate environmental agencies and as such, Arconic no longer provides these guarantees. In December 2016, Arconic entered into a one -year claims purchase agreement with a bank covering claims up to $245 related to the Saudi Arabian joint venture and two long-term energy supply agreements. The majority of the premium was paid by Alcoa Corporation. The agreement matured in December 2017 and was not renewed in 2018 due to the decline in exposure to guarantee claims including a substantial reduction in the guarantees related to the Saudi Arabian joint venture and also the elimination of the guarantee related to the Rockdale energy contract. The decision to enter into a claims purchase agreement will be made on an annual basis going forward. Letters of Credit. Arconic has outstanding letters of credit primarily related to workers’ compensation, energy contracts and leasing obligations. The total amount committed under these letters of credit, which automatically renew or expire at various dates, mostly in 2018, was $120 at December 31, 2017. Pursuant to the Separation and Distribution Agreement, Arconic was required to retain letters of credit of $62 that had previously been provided related to both Arconic and Alcoa Corporation workers’ compensation claims which occurred prior to November 1, 2016. Alcoa Corporation workers’ compensation claims and letter of credit fees paid by Arconic are being proportionally billed to and are being fully reimbursed by Alcoa Corporation. Additionally, Arconic was required to provide letters of credit for certain Alcoa Corporation equipment leases and energy contracts and, as a result, Arconic had $103 of outstanding letters of credit relating to these liabilities. The entire $103 of outstanding letters of credit were canceled in 2017 when Alcoa Corporation issued its own letters of credit to cover these obligations. Surety Bonds. Arconic has outstanding surety bonds primarily related to tax matters, contract performance, workers’ compensation, environmental-related matters, and customs duties. The total amount committed under these bonds, which automatically renew or expire at various dates, mostly in 2018, was $54 at December 31, 2017 . Pursuant to the Separation and Distribution Agreement, Arconic was required to provide surety bonds related to Alcoa Corporation workers’ compensation claims which occurred prior to November 1, 2016 and, as a result, Arconic has $25 in outstanding surety bonds relating to these liabilities. Alcoa Corporation workers’ compensation claims and surety bond fees paid by Arconic are being proportionately billed to and are being fully reimbursed by Alcoa Corporation.

Other Income, Net

Other Income, Net	12 Months Ended
	Dec. 31, 2017
Other Income and Expenses [Abstract]
Other Income, Net	Other Income, Net 2017 2016 2015 Equity income $ — $ (7 ) $ — Interest income (19 ) (16 ) (16 ) Foreign currency (gains) losses, net (5 ) (4 ) 51 Net (gain) loss from asset sales (513 ) 11 (42 ) Net loss (gain) on mark-to-market derivative contracts — 1 (3 ) Other, net (103 ) (79 ) (18 ) $ (640 ) $ (94 ) $ (28 ) In 2017, Net gain from assets sales included a gain on the sale of a portion of Arconic’s investment in Alcoa Corporation common stock of $351 (see Note C) and a gain of $167 on the Debt-for-Equity Exchange (see Note I). In 2017, Other, net included an adjustment of $81 to the contingent earn-out liability related to the 2014 acquisition of Firth Rixson (see Note F) and an adjustment of $25 associated with a separation-related guarantee liability (see Note K). In 2016, Other, net included an adjustment of $56 to the contingent earn-out liability and a post-closing adjustment of $20 , both related to the acquisition of Firth Rixson. In 2015, Net gain from asset sales included a gain of $19 related to the sale of land around Arconic’s former Sherwin, TX site and a gain of $19 related to the sale of the remaining equity investment in a China rolling mill.

Cash Flow Information

Cash Flow Information	12 Months Ended
	Dec. 31, 2017
Supplemental Cash Flow Information [Abstract]
Cash Flow Information	Cash Flow Information Cash paid for interest and income taxes was as follows: 2017 2016 2015 Interest, net of amount capitalized $ 508 $ 524 $ 487 Income taxes, net of amount refunded $ 118 $ 324 $ 345 The details related to cash paid for acquisitions were as follows: 2017 2016 2015 Assets acquired $ — $ — $ 2,003 Liabilities assumed — — (868 ) Equity issued — — (870 ) Working capital adjustment — (10 ) — Increase in Arconic’s shareholders’ equity — — (60 ) Cash paid — (10 ) 205 Less: cash acquired — — 302 Net cash paid $ — $ (10 ) $ (97 ) During 2016, Arconic sold various securities held by its captive insurance company for $130 , and an equity interest in a natural gas pipeline of $145 (Alcoa Corporation), both of which were included in Sales of investments on the accompanying Statement of Consolidated Cash Flows. In 2016, Arconic received $457 in proceeds from the redemption of certain company-owned life insurance policies, sold its Intalco smelter wharf property (Alcoa Corporation) for $120 , and sold the Remmele Medical business (see Note F) for $102 . These amounts were included in Proceeds from the sale of assets and businesses on the accompanying Statement of Consolidated Cash Flows. Noncash Financing and Investing Activities. On October 2, 2017, all outstanding 24,975,978 depositary shares (each depositary share representing a 1/10th interest in a share of the mandatory convertible preferred stock) were converted at a rate of 1.56996 into 39,211,286 common shares; 24,022 depositary shares were previously tendered for early conversion into 31,420 shares of Arconic common stock. No gain or loss was recognized associated with this equity transaction (see Note O). In the second quarter of 2017, the Company completed the Debt-for-Equity Exchange with the Investment Banks of the remaining portion of Arconic’s retained interest in Alcoa Corporation common stock for a portion of the Company’s outstanding notes held by the Investment Banks for $465 including accrued and unpaid interest (see Note I). On October 5, 2016, Arconic completed a 1-for- 3 Reverse Stock Split (see Note O). The Reverse Stock Split reduced the number of shares of common stock outstanding from approximately 1.3 billion shares to approximately 0.4 billion shares. The par value of the common stock remained at $1.00 per share. Accordingly, Common stock and Additional capital in the Company’s Consolidated Balance Sheet at December 31, 2016 reflect a decrease and increase of $877 , respectively. In August 2016, Arconic retired its outstanding treasury stock consisting of approximately 76 million shares (see Note O). As a result, Common stock and Additional capital were decreased by $76 and $2,563 , respectively, to reflect the retirement of the treasury shares. In July 2015, Arconic purchased all outstanding shares of RTI common stock in a stock-for-stock transaction valued at $870 (see Note F). As a result, Arconic issued 29 million shares ( 87 million shares—pre-Reverse Stock Split—see Note O) of its common stock to consummate this transaction.

Segment and Geographic Area Inf

Segment and Geographic Area Information	12 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
Segment and Geographic Area Information	Segment and Geographic Area Information Arconic is a global leader in lightweight metals engineering and manufacturing. Arconic’s innovative, multi-material products, which include aluminum, titanium, and nickel, are used worldwide in aerospace, automotive, commercial transportation, packaging, building and construction, oil and gas, defense, consumer electronics, and industrial applications. Arconic’s segments are organized by product on a worldwide basis. In the first quarter of 2017, the Company changed its primary measure of segment performance from After-tax operating income (ATOI) to Adjusted earnings before interest, tax, depreciation and amortization (“Adjusted EBITDA”). Segment performance under Arconic’s management reporting system is evaluated based on a number of factors; however, the primary measure of performance in 2017 was Adjusted EBITDA. Arconic’s definition of Adjusted EBITDA is net margin plus an add-back for depreciation and amortization. Net margin is equivalent to Sales minus the following items: Cost of goods sold; Selling, general administrative, and other expenses; Research and development expenses; and Provision for depreciation and amortization. Prior period information has been recast to conform to current year presentation. The Adjusted EBITDA presented may not be comparable to similarly titled measures of other companies. Items required to reconcile Combined segment adjusted EBITDA to Net loss attributable to Arconic include: the Provision for depreciation and amortization; Impairment of goodwill; Restructuring and other charges; the impact of LIFO inventory accounting; metal price lag (the timing difference created when the average price of metal sold differs from the average cost of the metal when purchased by the respective segment — generally, when the price of metal increases, metal price lag is favorable, and when the price of metal decreases, metal price lag is unfavorable); corporate expense (general administrative and selling expenses of operating the corporate headquarters and other global administrative facilities and corporate research and development expenses); other items, including intersegment profit eliminations; Other income, net; Interest expense; Income tax expense; and the results of discontinued operations. The accounting policies of the segments are the same as those described in the Summary of Significant Accounting Policies (see Note A). Transactions among segments are established based on negotiation among the parties. Differences between segment totals and Arconic’s consolidated totals for line items not reconciled are in Corporate. Arconic’s operations consist of three worldwide reportable segments as follows: Engineered Products and Solutions. This segment produces products that are used mostly in the aerospace (commercial and defense), industrial, commercial transportation, and power generation end markets. Such products include fastening systems (titanium, steel, and nickel superalloys) and seamless rolled rings (mostly nickel superalloys); investment castings (nickel superalloys, titanium, and aluminum), including airfoils and forged jet engine components (e.g., jet engine disks); and extruded, machined and formed aircraft parts (titanium and aluminum), all of which are sold directly to customers and through distributors. More than 75% of the third-party sales in this segment are from the aerospace end market. A small part of this segment also produces various forged, extruded, and machined metal products (titanium, aluminum and steel) for the oil and gas, automotive, and land and sea defense end markets. Seasonal decreases in sales are generally experienced in the third quarter of the year due to the European summer slowdown across all end markets. Global Rolled Products. This segment produces aluminum sheet and plate for a variety of end markets. This segment includes sheet and plate sold directly to customers and through distributors in the aerospace, automotive, commercial transportation, packaging, building and construction, and industrial products (mainly used in the production of machinery and equipment and consumer durables) end markets. A small portion of this segment also produces aseptic foil for the packaging end market. While the customer base for flat-rolled products is large, a significant amount of sales of sheet and plate is to a relatively small number of customers. Transportation and Construction Solutions. This segment produces products that are used mostly in the commercial transportation and nonresidential building and construction end markets. Such products include integrated aluminum structural systems, architectural extrusions, and forged aluminum commercial vehicle wheels, which are sold directly to customers and through distributors. A small part of this segment also produces aluminum products for the industrial products end market. The operating results and assets of Arconic’s reportable segments were as follows: Engineered Products and Solutions Global Rolled Products Transportation and Construction Solutions Total 2017 Sales: Third-party sales $ 5,935 $ 4,992 $ 1,985 $ 12,912 Intersegment sales — 148 — 148 Total sales $ 5,935 $ 5,140 $ 1,985 $ 13,060 Profit and loss: Depreciation and amortization 268 205 50 523 Adjusted EBITDA 1,224 599 321 2,144 2016 Sales: Third-party sales $ 5,728 $ 4,864 $ 1,802 $ 12,394 Intersegment sales — 118 — 118 Total sales $ 5,728 $ 4,982 $ 1,802 $ 12,512 Profit and loss: Depreciation and amortization $ 255 $ 201 $ 48 $ 504 Adjusted EBITDA 1,195 577 291 2,063 2015 Sales: Third-party sales $ 5,342 $ 5,253 $ 1,882 $ 12,477 Intersegment sales — 125 — 125 Total sales $ 5,342 $ 5,378 $ 1,882 $ 12,602 Profit and loss: Depreciation and amortization $ 233 $ 203 $ 43 $ 479 Adjusted EBITDA 1,111 512 271 1,894 2017 Assets: Capital expenditures $ 308 $ 178 $ 57 $ 543 Goodwill 3,949 193 60 4,202 Total assets 10,252 4,179 1,068 15,499 2016 Assets: Capital expenditures $ 333 $ 293 $ 63 $ 689 Goodwill 4,579 181 57 4,817 Total assets 10,542 3,891 982 15,415 The following tables reconcile certain segment information to consolidated totals: 2017 2016 2015 Sales: Total segment sales $ 13,060 $ 12,512 $ 12,602 Elimination of intersegment sales (148 ) (118 ) (125 ) Corporate 48 — (64 ) Consolidated sales $ 12,960 $ 12,394 $ 12,413 2017 2016 2015 Combined segment adjusted EBITDA $ 2,144 $ 2,063 $ 1,894 Unallocated amounts: Depreciation and amortization (551 ) (535 ) (508 ) Impairment of goodwill (719 ) — (25 ) Restructuring and other charges (165 ) (155 ) (214 ) Impact of LIFO (110 ) (18 ) 101 Metal price lag 72 27 (175 ) Corporate expense (274 ) (454 ) (371 ) Other (71 ) (109 ) (74 ) Operating income 326 819 628 Interest expense (496 ) (499 ) (473 ) Other income, net 640 94 28 Income from continuing operations before income taxes 470 414 183 Provision for income taxes (544 ) (1,476 ) (339 ) Discontinued operations — 121 (165 ) Net income attributable to noncontrolling interest — — (1 ) Net loss attributable to Arconic $ (74 ) $ (941 ) $ (322 ) December 31, 2017 2016 Assets: Total segment assets $ 15,499 $ 15,415 Unallocated amounts: Cash and cash equivalents 2,150 1,863 Deferred income taxes 743 1,234 Corporate goodwill 333 331 Corporate fixed assets, net 310 308 LIFO reserve (481 ) (371 ) Fair value of derivative contracts 91 24 Investment in common stock of Alcoa Corporation — 1,020 Other 73 214 Consolidated assets $ 18,718 $ 20,038 Sales by major product grouping were as follows: 2017 2016 2015 Sales: Flat-rolled aluminum $ 4,992 $ 4,864 $ 5,253 Fastening systems and rings 2,102 2,060 2,168 Investment castings 1,983 1,870 1,812 Other extruded and forged products 1,565 1,495 1,332 Architectural aluminum systems 1,065 1,010 951 Aluminum wheels 805 689 790 Other 448 406 107 $ 12,960 $ 12,394 $ 12,413 Geographic information for sales was as follows (based upon the country where the point of sale occurred): 2017 2016 2015 Sales: United States $ 8,167 $ 7,823 $ 8,044 France 965 930 802 Hungary 739 619 622 United Kingdom 721 711 698 China 615 582 565 Russia 500 433 455 Germany 309 284 264 Brazil 285 250 297 Canada 261 262 180 Japan 141 145 138 Italy 37 127 139 Other 220 228 209 $ 12,960 $ 12,394 $ 12,413 Geographic information for long-lived assets was as follows (based upon the physical location of the assets): December 31, 2017 2016 Long-lived assets: United States $ 4,005 $ 3,966 China 347 336 Russia 276 295 United Kingdom 259 232 Hungary 227 194 France 159 118 Germany 88 64 Canada 63 58 Brazil 62 97 Other 108 139 $ 5,594 $ 5,499

Preferred and Common Stock

Preferred and Common Stock	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Preferred and Common Stock	Preferred and Common Stock Preferred Stock. Arconic has two classes of preferred stock: Class A Preferred Stock and Class B Serial Preferred Stock. Class A Preferred Stock has 660,000 shares authorized at a par value of $100 per share with an annual 3.75 cumulative dividend preference per share. There were 546,024 of such shares outstanding at December 31, 2017 and 2016 . Class B Serial Preferred Stock has 10,000,000 shares authorized at a par value of $1 per share. There were no shares outstanding at December 31, 2017 and 2,500,000 of such shares outstanding at December 31, 2016 (see below). In September 2014, Arconic completed a public offering under its shelf registration statement for $1,250 of 25 million depositary shares, each of which represents a 1/10th interest in a share of Arconic’s 5.375% Class B Mandatory Convertible Preferred Stock, Series 1, par value $1 per share, liquidation preference $500 per share (the “Mandatory Convertible Preferred Stock”). The 25 million depositary shares are equivalent to 2.5 million shares of Mandatory Convertible Preferred Stock. Each depositary share entitled the holder, through the depositary, to a proportional fractional interest in the rights and preferences of a share of Mandatory Convertible Preferred Stock, including conversion, dividend, liquidation, and voting rights, subject to terms of the deposit agreement. Arconic received $1,213 in net proceeds from the public offering reflecting an underwriting discount. The net proceeds were used, together with the net proceeds of issued debt, to finance the cash portion of the acquisition of Firth Rixson. The underwriting discount was recorded as a decrease to Additional capital. The Mandatory Convertible Preferred Stock constitutes a series of Arconic’s Class B Serial Preferred Stock, which ranks senior to Arconic’s common stock and junior to Arconic’s Class A Preferred Stock and existing and future indebtedness. Holders of the Mandatory Convertible Preferred Stock generally have no voting rights. Dividends on the Mandatory Convertible Preferred Stock were cumulative in nature and paid at the rate of $26.8750 per annum per share in 2016 and 2015, which commenced January 1, 2015 (paid on December 30, 2014). On October 2, 2017, all outstanding 24,975,978 depositary shares were converted at a rate of 1.56996 into 39,211,286 common shares; 24,022 depositary shares were previously tendered for early conversion into 31,420 shares of Arconic common stock. No gain or loss was recognized associated with this equity transaction. Dividends on the Mandatory Convertible Preferred Stock were paid at the rate of $20.1563 per share in 2017. Common Stock. Pursuant to the authorization provided at a special meeting of Arconic common shareholders held on October 5, 2016, shareholders approved a 1-for-3 reverse stock split of Arconic’s outstanding and authorized shares of common stock (the “Reverse Stock Split”). As a result of the Reverse Stock Split, every three shares of issued and outstanding common stock were combined into one issued and outstanding share of common stock. The Reverse Stock Split reduced the number of shares of common stock outstanding from approximately 1.3 billion shares to approximately 0.4 billion shares. The par value of the common stock remained at $1 per share. Accordingly, Common stock and Additional capital in the accompanying Consolidated Balance Sheet at December 31, 2016 reflected a decrease and increase of $877 , respectively. The number of authorized shares of common stock was also decreased from 1.8 billion shares to 0.6 billion shares. The Company’s common stock began trading on a reverse stock split-adjusted basis on the NYSE on October 6, 2016. In August 2016, Arconic retired its outstanding treasury stock consisting of approximately 25 million shares ( 76 million shares pre-Reverse Stock Split). As a result, Common stock and Additional capital in the accompanying 2016 Consolidated Balance Sheet were decreased by $76 and $2,563 , respectively, to reflect the retirement of the treasury shares. As of December 31, 2017 and 2016, there was no outstanding treasury stock. At December 31, 2017 , 481,416,537 shares were issued and outstanding. Dividends paid in 2017 were $0.24 per annum or $0.06 per quarter and $0.36 per annum or $0.09 per quarter in 2016 and 2015 . The current dividend yield as authorized by Arconic’s Board of Directors is $0.24 per annum or $0.06 per quarter. In July 2015, Arconic issued 29 million shares ( 87 million shares—pre-Reverse Stock Split) of common stock as consideration paid to acquire RTI (see Note F). Additionally, Arconic assumed the obligation to repay two tranches of convertible debt; one tranche was due and settled in cash on December 1, 2015 (principal amount of $115 ) and the other tranche is due on October 15, 2019 (principal amount of $403 ), unless earlier converted or purchased by Arconic at the holder’s option under specific conditions. Upon conversion of the 2019 convertible notes, holders will receive, at Arconic’s election, cash, shares of common stock (approximately 14,294,000 shares using the December 31, 2017 conversion rate of 35.5119 shares per $1,000 (not in millions) bond or per-share conversion price of $28.1596 ), or a combination of cash and shares. On the maturity date, each holder of outstanding notes will be entitled to receive on such date $1,000 (not in millions) in cash for each $1,000 (not in millions) bond, together with accrued and unpaid interest. As of December 31, 2017 , 47 million shares of common stock were reserved for issuance under Arconic’s stock-based compensation plans. As of December 31, 2017, 43 million shares remain available for issuance. Arconic issues new shares to satisfy the exercise of stock options and the conversion of stock awards. Share Activity (number of shares) Common stock Treasury Outstanding Balance at end of 2014 87,150,169 1,216,663,661 Issued for stock-based compensation plans (6,099,066 ) 6,099,066 Acquisition of RTI — 87,397,414 Balance at end of 2015 81,051,103 1,310,160,141 Issued for stock-based compensation plans (5,219,660 ) 5,302,128 Treasury stock retirement (75,831,443 ) — Reverse Stock Split — (876,942,489 ) Balance at end of 2016 — 438,519,780 Conversion of convertible notes — 39,242,706 Issued for stock-based compensation plans — 3,654,051 Balance at end of 2017 — 481,416,537 Stock-based Compensation Arconic has a stock-based compensation plan under which stock options and restricted stock unit awards are granted in January each year to eligible employees. Most plan participants can choose whether to receive their award in the form of stock options, restricted stock unit awards, or a combination of both. This choice is made before the grant is issued and is irrevocable. Stock options are granted at the closing market price of Arconic’s common stock on the date of grant and vest over a three -year service period (1/3 each year) with a ten -year contractual term. Restricted stock unit awards typically vest over a three -year service period from the date of grant. Certain of these awards also include performance and market conditions. For the majority of performance stock awards issued in 2017 , 2016 , and 2015 , the final number of shares earned will be based on Arconic’s achievement of sales and profitability targets over the respective three -year performance periods. For awards issued in 2017, the award will be earned at the end of the three-year performance period. For awards issued in 2016 and 2015, one-third of the award will be earned each year based on the performance against the pre-established targets for that year. The performance stock awards earned over the three-year period vest at the end of the third year. Additionally, the 2017 awards will be scaled by a total shareholder return (“TSR”) multiplier, which depends upon relative three -year performance against the TSRs of a group of peer companies. In 2017 , 2016 and 2015 , Arconic recognized stock-based compensation expense of $54 ( $36 after-tax), $76 ( $51 after-tax), and $77 ( $51 after-tax), respectively. The expense related to restricted stock unit awards in 2017 , 2016 and 2015 was approximately 85% , 80% and 80% , respectively. No stock-based compensation expense was capitalized in any of those years. 2017 stock-based compensation expense was reduced by $13 for certain executive pre-vest cancellations which were recorded in Restructuring and other charges within the Statement of Consolidated Operations. At December 31, 2017 , there was $43 (pre-tax) of unrecognized compensation expense related to non-vested stock option grants and non-vested restricted stock unit award grants. This expense is expected to be recognized over a weighted average period of 1.6 years. As part of Arconic’s stock-based compensation plan design, individuals who are retirement-eligible have a six-month requisite service period in the year of grant. As a result, a larger portion of expense will be recognized in the first half of each year for these retirement-eligible employees. Of the total pre-tax compensation expense recognized in 2017 , 2016 and 2015 , $15 , $19 , and $15 , respectively, pertains to the acceleration of expense related to retirement-eligible employees. Stock-based compensation expense is based on the grant date fair value of the applicable equity grant. For restricted stock unit awards, the fair value was equivalent to the closing market price of Arconic’s common stock on the date of grant. The grant date fair value of the 2017 performance awards containing a market condition was $21.99 and was valued using a Monte Carlo model. A Monte Carlo simulation uses assumptions of stock price behavior to estimate the probability of satisfying market conditions and the resulting fair value of the award. The risk-free interest rate ( 1.5% ) was based on a yield curve of interest rates at the time of the grant based on the remaining performance period. Because of limited historical information due to the Separation Transaction, volatility ( 38.0% ) was estimated using implied volatility and the representative price return approach, which uses price returns of comparable companies to develop a correlation assumption. For stock options, the fair value was estimated on the date of grant using a lattice-pricing model, which generated a result of $6.26 , $4.78 , and $10.07 per option in 2017 , 2016 , and 2015 , respectively. The lattice-pricing model uses a number of assumptions to estimate the fair value of a stock option, including a risk-free interest rate, dividend yield, volatility, exercise behavior, and contractual life. The following paragraph describes in detail the assumptions used to estimate the fair value of stock options granted in 2017 (the assumptions used to estimate the fair value of stock options granted in 2016 and 2015 were not materially different, except as noted below). The risk-free interest rate ( 2.4% ) was based on a yield curve of interest rates at the time of the grant based on the contractual life of the option. The dividend yield ( 1.2% ) was based on a one-year average. Volatility ( 38.1% for 2017 , 44.5% for 2016 , and 36.5% in 2015 ) was based on historical volatilities (except 2017 where we used comparable companies) and implied volatilities over the term of the option. Arconic utilized historical option forfeiture data to estimate annual pre- and post-vesting forfeitures ( 6% ). Exercise behavior ( 59% ) was based on a weighted average exercise ratio (exercise patterns for grants issued over the number of years in the contractual option term) of an option’s intrinsic value resulting from historical employee exercise behavior. Based upon the other assumptions used in the determination of the fair value, the life of an option ( 5.9 years) was an output of the lattice-pricing model. The activity for stock options and stock awards during 2017 was as follows (options and awards in millions): Stock options Stock awards Number of options Weighted average exercise price Number of awards Weighted average FMV per award Outstanding, January 1, 2017 13 $ 24.14 8 $ 22.26 Granted 2 21.13 3 21.86 Exercised (2 ) 20.65 — — Converted — — (2 ) 24.95 Expired or forfeited (2 ) 25.99 (2 ) 21.26 Performance share adjustment — — — 21.48 Outstanding, December 31, 2017 11 23.94 7 21.49 As of December 31, 2017 , the number of stock options outstanding had a weighted average remaining contractual life of 5.3 years and a total intrinsic value of $53 . Additionally, 7.4 million of the stock options outstanding were fully vested and exercisable and had a weighted average remaining contractual life of 4.2 years, a weighted average exercise price of $25.90 , and a total intrinsic value of $26 as of December 31, 2017 . In 2017 , 2016 and 2015 , the cash received from stock option exercises was $50 , $4 , and $25 and the total tax benefit realized from these exercises was $4 , $0 , and $6 , respectively. The total intrinsic value of stock options exercised during 2017 , 2016 and 2015 was $13 , $1 , and $19 , respectively.

Earnings Per Share

Earnings Per Share	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Earnings Per Share	Earnings Per Share Basic earnings per share (EPS) amounts are computed by dividing earnings (loss), after the deduction of preferred stock dividends declared, by the average number of common shares outstanding. Diluted EPS amounts assume the issuance of common stock for all potentially dilutive share equivalents outstanding. The number of shares and per share amounts for all periods presented below have been updated to reflect the Reverse Stock Split (see Note O). The information used to compute basic and diluted EPS attributable to Arconic common shareholders was as follows (shares in millions): 2017 2016 2015 Net loss from continuing operations attributable to Arconic $ (74 ) $ (1,062 ) $ (156 ) Net income from continuing operations attributable to noncontrolling interests — — (1 ) Less: preferred stock dividends declared (53 ) (69 ) (69 ) Loss from continuing operations available to Arconic common shareholders (127 ) (1,131 ) (226 ) Income (loss) from discontinued operations after income taxes and noncontrolling interests (1) — 121 (165 ) Net loss available to Arconic common shareholders—basic (127 ) (1,010 ) (391 ) Add: interest expense related to convertible notes — — — Add: dividends related to mandatory convertible preferred stock — — — Net loss available to Arconic common shareholders—diluted $ (127 ) $ (1,010 ) $ (391 ) Average shares outstanding—basic 451 438 420 Effect of dilutive securities: Stock options — — — Stock and performance awards — — — Mandatory convertible preferred stock — — — Convertible notes — — — Average shares outstanding—diluted 451 438 420 (1) Calculated from the Statement of Consolidated Operations as Income (loss) from discontinued operations after income taxes less Net income from discontinued operations attributable to noncontrolling interests. In 2017, basic average shares outstanding and diluted average shares outstanding were the same because the effect of potential shares of common stock was anti-dilutive as Arconic generated a net loss. As a result, 39 million share equivalents related to the mandatory convertible preferred stock, 14 million (weighted average) share equivalents related to convertible notes (acquired from RTI - see Note O), 11 million stock options, and 7 million stock awards were not included in the computation of diluted EPS. Had Arconic generated sufficient net income in 2017, 30 million , 14 million , 5 million , and 1 million potential shares of common stock related to the mandatory convertible preferred stock, convertible notes, stock awards, and stock options, respectively, would have been included in diluted average shares outstanding. The mandatory convertible preferred stock converted on October 2, 2017 (see Note O). In 2016, basic average shares outstanding and diluted average shares outstanding were the same because the effect of potential shares of common stock was anti-dilutive as Arconic generated a net loss. As a result, 39 million share equivalents related to the mandatory convertible preferred stock, 14 million share equivalents related to convertible notes, 13 million stock options, and 8 million stock awards were not included in the computation of diluted EPS. Had Arconic generated sufficient net income in 2016, 28 million , 10 million , 4 million , and 1 million potential shares of common stock related to the mandatory convertible preferred stock, convertible notes, stock awards, and stock options, respectively, would have been included in diluted average shares outstanding. In 2015, basic average shares outstanding and diluted average shares outstanding were the same because the effect of potential shares of common stock was anti-dilutive as Arconic generated a net loss. As a result, 26 million share equivalents related to mandatory convertible preferred stock, 7 million stock awards, 11 million stock options, and 5 million share equivalents related to convertible notes were not included in the computation of diluted EPS. Had Arconic generated sufficient net income in 2015, 26 million , 5 million , 4 million , and 1 million potential shares of common stock related to the mandatory convertible preferred stock, convertible notes, stock awards, and stock options, respectively, would have been included in diluted average shares outstanding. Options to purchase 3 million , 10 million , and 9 million shares of common stock at a weighted average exercise price of $33.32 , $26.93 , and $38.25 per share were outstanding as of December 31, 2017 , 2016 , and 2015 , respectively, but were not included in the computation of diluted EPS because they were anti-dilutive, as the exercise prices of the options were greater than the average market price of Arconic’s common stock.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The components of income from continuing operations before income taxes were as follows: 2017 2016 2015 United States $ 500 $ 84 $ 124 Foreign (30 ) 330 59 $ 470 $ 414 $ 183 The provision for income taxes consisted of the following: 2017 2016 2015 Current: Federal* $ — $ — $ — Foreign 98 133 115 State and local (2 ) 1 (1 ) 96 134 114 Deferred: Federal* 489 1,208 196 Foreign 37 136 29 State and local (78 ) (2 ) — 448 1,342 225 Total $ 544 $ 1,476 $ 339 * Includes U.S. taxes related to foreign income The exercise of employee stock options generated a tax charge of $1 in 2017 and a benefit of $0 and $2 in 2016 and 2015 , respectively, representing only the difference between compensation expense recognized for financial reporting and tax purposes. The tax effects related to the exercise of employee stock options in 2017 were recorded to the income statement within the provision for income taxes. Tax effects related to 2016 and 2015 were recorded to equity. Payments either decreased current taxes payable or increased deferred tax assets (net operating losses) in the respective periods. Arconic has unamortized tax-deductible goodwill of $24 resulting from intercompany stock sales and reorganizations. Arconic recognizes the tax benefits (at a 25% rate) associated with this tax-deductible goodwill as it is being amortized for local income tax purposes rather than in the period in which the transaction is consummated. A reconciliation of the U.S. federal statutory rate to Arconic’s effective tax rate was as follows (the effective tax rate for all periods was a provision on income): 2017 2016 2015 U.S. federal statutory rate 35.0 % 35.0 % 35.0 % Taxes on foreign operations (7.5 ) (10.2 ) 2.5 Federal benefit of state tax 3.1 0.4 0.3 Permanent differences on restructuring and other charges and asset disposals (1) (167.4 ) (107.8 ) 3.6 Non-deductible acquisition costs 0.3 8.4 7.1 Statutory tax rate and law changes (2) 52.5 (15.7 ) (1.0 ) Tax holidays (3.0 ) (0.8 ) (3.9 ) Tax credits (0.7 ) (1.2 ) (2.8 ) Changes in valuation allowances 137.9 426.8 145.8 Impairment of goodwill 53.5 — 4.8 Company-owned life insurance/split-dollar net premiums — 23.0 (3.0 ) Changes in uncertain tax positions 10.1 2.1 (2.2 ) Other 1.9 (3.5 ) (1.0 ) Effective tax rate 115.7 % 356.5 % 185.2 % (1) Additional losses were reported in Spain's 2017 tax return related to the Separation Transaction which are offset by an increased valuation allowance. (2) On December 22, 2017, the United States enacted the Tax Cuts and Jobs Act of 2017 ("the 2017 Act”) resulting in significant changes to the Internal Revenue Code (see below). In December 2016, Spain and the United States enacted tax law changes which resulted in the remeasurement of certain deferred tax liabilities recorded by Arconic. On December 22, 2017, the 2017 Act was signed into law, making significant changes to the Internal Revenue Code. Changes include, but are not limited to, a corporate tax rate decrease from 35% to 21% effective for tax years beginning after December 31, 2017, the transition of U.S. international taxation from a worldwide tax system to a territorial system, and a one-time transition tax on the non-previously taxed post-1986 foreign earnings and profits of certain U.S.-owned foreign corporations as of December 31, 2017. Also on December 22, 2017, Staff Accounting Bulletin No. 118 ("SAB 118"), Income Tax Accounting Implications of the Tax Cuts and Jobs Act, was issued by the Securities and Exchange Commission to address the application of U.S. GAAP for financial reporting. SAB 118 permits the use of provisional amounts based on reasonable estimates in the financial statements. SAB 118 also provides that the tax impact may be considered incomplete in situations when a registrant does not have the necessary information available, prepared, or analyzed (including computations) in reasonable detail to complete the accounting for certain income tax effects of the 2017 Act. Any adjustments to provisional or incomplete amounts should be included in income from continuing operations as an adjustment to tax expense or benefit in the reporting period that the amounts are determined within one year. As of February 2, 2018, the Company has calculated a reasonable estimate of the impact of the 2017 Act’s tax rate reduction and one-time transition tax in its year end income tax provision in accordance with its understanding of the 2017 Act and guidance available and, as a result, has recorded a $272 tax charge in the fourth quarter of 2017, the period in which the legislation was enacted. We anticipate finalizing our accounting during 2018 in accordance with SAB 118. U.S. deferred tax assets and liabilities as of the date of enactment of the 2017 Act are based on estimated temporary differences which will be updated and finalized with the filing of the 2017 U.S. income tax return. Changes to the estimated temporary differences will result in changes to the revaluation of the deferred tax assets and liabilities. As such, the impact of the 2017 Act’s tax rate reduction is a provisional amount under SAB 118 which will be updated during 2018. The impact of the one-time transition tax on the deemed repatriation of non-previously taxed post-1986 foreign earnings and profits of certain U.S.-owned foreign corporations, net of foreign tax credits, is also considered a provisional amount. The Company will continue to analyze the amount of foreign earnings and profits, the associated foreign tax credits, and additional guidance that may be issued during 2018 and will update the estimated deemed repatriation calculation as necessary under SAB 118. The Company has not yet gathered, prepared and analyzed all the necessary information in sufficient detail to determine whether any excess foreign tax credits that may result from the deemed repatriation will be realizable. The need for additional valuation allowance on foreign tax credits that may not be more likely than not to be realized in the future will be reassessed during 2018. The components of net deferred tax assets and liabilities were as follows: 2017 2016 December 31, Deferred tax assets Deferred tax liabilities Deferred tax assets Deferred tax liabilities Depreciation $ 31 $ 693 $ 15 $ 817 Employee benefits 936 23 1,382 8 Loss provisions 134 14 181 1 Deferred income/expense 19 1,144 20 74 Tax loss carryforwards 3,305 — 1,540 — Tax credit carryforwards 638 — 652 — Other 24 33 164 19 5,087 1,907 3,954 919 Valuation allowance (2,584 ) — (1,940 ) — $ 2,503 $ 1,907 $ 2,014 $ 919 The following table details the expiration periods of the deferred tax assets presented above: December 31, 2017 Expires within 10 years Expires within 11-20 years No expiration* Other* Total Tax loss carryforwards $ 81 $ 781 $ 2,443 $ — $ 3,305 Tax credit carryforwards 531 97 10 — 638 Other — — 84 1,060 1,144 Valuation allowance (467 ) (646 ) (1,376 ) (95 ) (2,584 ) $ 145 $ 232 $ 1,161 $ 965 $ 2,503 * Deferred tax assets with no expiration may still have annual limitations on utilization. Other represents deferred tax assets whose expiration is dependent upon the reversal of the underlying temporary difference. A substantial amount of Other relates to employee benefits that will become deductible for tax purposes over an extended period of time as contributions are made to employee benefit plans and payments are made to retirees. The total deferred tax asset (net of valuation allowance) is supported by projections of future taxable income exclusive of reversing temporary differences ( 30% ) and taxable temporary differences that reverse within the carryforward period ( 70% ). Valuation allowances are recorded to reduce deferred tax assets when it is more likely than not (greater than 50% ) that a tax benefit will not be realized. In evaluating the need for a valuation allowance, management considers all potential sources of taxable income, including income available in carryback periods, future reversals of taxable temporary differences, projections of taxable income, and income from tax planning strategies, as well as all available positive and negative evidence. Positive evidence includes factors such as a history of profitable operations, projections of future profitability within the carryforward period, including from tax planning strategies, and Arconic’s experience with similar operations. Existing favorable contracts and the ability to sell products into established markets are additional positive evidence. Negative evidence includes items such as cumulative losses, projections of future losses, or carryforward periods that are not long enough to allow for the utilization of a deferred tax asset based on existing projections of income. Deferred tax assets for which no valuation allowance is recorded may not be realized upon changes in facts and circumstances, resulting in a future charge to establish a valuation allowance. Existing valuation allowances are re-examined under the same standards of positive and negative evidence. If it is determined that it is more likely than not that a deferred tax asset will be realized, the appropriate amount of the valuation allowance, if any, is released. Deferred tax assets and liabilities are also re-measured to reflect changes in underlying tax rates due to law changes and the granting and lapse of tax holidays. In 2017, Arconic released $98 of certain U.S. state valuation allowances. After weighing all available positive and negative evidence, management determined that the underlying net deferred tax assets were more likely than not realizable based on projected taxable income estimates taking into account expected post-separation apportionment data. Valuation allowances of $750 remain against other net state deferred tax assets expected to expire before utilization. The need for valuation allowances against net state deferred tax assets will be reassessed on a continuous basis in future periods and, as a result, the allowance may increase or decrease based on changes in facts and circumstances. Arconic also recorded an additional valuation allowance of $675 which offsets additional losses reported on the Spanish tax return filed in 2017 related to the Separation Transaction that are not more likely than not to be realized. There is no net impact to the provision for income taxes, as the additional valuation allowance fully offsets the current year tax benefit in Spain . Arconic’s foreign tax credits in the United States have a 10 -year carryforward period with expirations ranging from 2018 to 2027 (as of December 31, 2017). Valuation allowances were initially established in prior years on a portion of the foreign tax credit carryforwards, primarily due to insufficient foreign source income to allow for full utilization of the credits within the expiration period. After consideration of all available evidence including potential tax planning strategies and earnings of foreign subsidiaries projected to be distributable as taxable foreign dividends, incremental valuation allowances of $302 and $134 were recognized in 2016 and 2015, respectively. Foreign tax credits of $57 , $128 , and $15 expired at the end of 2017, 2016, and 2015, respectively, resulting in a corresponding decrease to the valuation allowance. During 2017, an additional valuation allowance of $23 was recorded for current year excess foreign tax credits, offset by a net $14 reduction for other adjustments. At December 31, 2017, the cumulative amount of the valuation allowance was $379 . The need for this valuation allowance will be reassessed on a continuous basis in future periods and, as a result, the allowance may increase or decrease based on changes in facts and circumstances, including the impact of the 2017 Act. Arconic will continue its analysis of the 2017 Act, including any additional guidance that may be issued. Further analysis could result in changes to assumptions related to the realizability of certain deferred tax assets including, but not limited to, foreign tax credits, alternative minimum tax credits, and state tax loss carryforwards. Provisional estimates of the impact of the 2017 Act on the realizability of certain deferred tax assets have been made based on information and computations that were available, prepared, and analyzed as of February 2, 2018. In accordance with SAB 118, Arconic will reassess the need for valuation allowances on these deferred tax assets as necessary during 2018. In 2016 , Arconic recognized a $1,267 discrete income tax charge for valuation allowances related to the Separation Transaction, including $925 with respect to Alcoa Corporation’s net deferred tax assets in the United States, $302 with respect to Arconic’s foreign tax credits in the United States, $42 with respect to certain deferred tax assets in Luxembourg, and $(2) related to the net impact of other smaller items. After weighing all positive and negative evidence, as described above, management determined that the net deferred tax assets of Alcoa Corporation were not more likely than not to be realized due to lack of historical and projected domestic source taxable income. As such, a valuation allowance was recorded immediately prior to separation. In addition, Arconic recognized a $42 discrete income tax charge in 2016 for a valuation allowance on the full value of certain net deferred tax assets in Luxembourg. Sources of taxable income which previously supported the net deferred tax asset are no longer available as a result of the Separation Transaction. The need for this valuation allowance will be reassessed on a continuous basis in future periods and, as a result, the allowance may increase or decrease based on changes in facts and circumstances. In 2016 , Arconic also recognized discrete income tax benefits related to the release of valuation allowances on certain net deferred tax assets in Russia and Canada of $19 and $20 , respectively. After weighing all available evidence, management determined that it was more likely than not that the net income tax benefits associated with the underlying deferred tax assets would be realizable based on historic cumulative income and projected taxable income. Arconic also recorded additional valuation allowances in Australia of $93 related to the Separation Transaction, in Spain of $163 related to a tax law change and in Luxembourg of $280 related to the Separation Transaction as well as a tax law change. These valuation allowances fully offset current year changes in deferred tax asset balances of each respective jurisdiction, resulting in no net impact to tax expense. The need for a valuation allowance will be reassessed on a continuous basis in future periods by each jurisdiction and, as a result, the allowances may increase or decrease based on changes in facts and circumstances. In 2015 , Arconic recognized an additional $141 discrete income tax charge for valuation allowances on certain deferred tax assets in Iceland and Suriname. Of this amount, an $85 valuation allowance was established on the full value of the deferred tax assets in Suriname, which were related mostly to employee benefits and tax loss carryforwards. These deferred tax assets have an expiration period ranging from 2016 to 2022 (as of December 31, 2015). The remaining $56 charge relates to a valuation allowance established on a portion of the deferred tax assets recorded in Iceland. These deferred tax assets have an expiration period ranging from 2017 to 2023 . After weighing all available positive and negative evidence, as described above, management determined that it was no longer more likely than not that Arconic will realize the tax benefit of either of these deferred tax assets. This was mainly driven by a decline in the outlook of the Primary Metals business, combined with prior year cumulative losses and a short expiration period. The following table details the changes in the valuation allowance: December 31, 2017 2016 2015 Balance at beginning of year $ 1,940 $ 1,291 $ 1,151 Increase to allowance 831 772 180 Release of allowance (246 ) (209 ) (42 ) Acquisitions and divestitures (F) (1 ) (1 ) 29 Tax apportionment, tax rate and tax law changes (24 ) 106 (15 ) Foreign currency translation 84 (19 ) (12 ) Balance at end of year $ 2,584 $ 1,940 $ 1,291 As a result of the 2017 Act, the non-previously taxed post-1986 foreign earnings and profits (calculated based on U.S. tax principles) of certain U.S.-owned foreign corporations has been subject to U.S. tax under the one-time transition tax provisions. The cumulative amount of Arconic’s foreign undistributed U.S. GAAP earnings is estimated to be less than the total foreign earnings and profits already subject to U.S. tax as of December 31, 2017. As such, Arconic expects to be able to repatriate these earnings back to the United States without additional income tax consequences other than foreign withholding taxes which will not have a material impact. At this time, management has no plans to distribute such earnings in the foreseeable future. The Company will continue to evaluate whether to repatriate all or a portion of the cumulative undistributed foreign earnings in light of the 2017 Act and consider that conclusion to be incomplete under SAB 118. The 2017 Act creates a new requirement that certain income earned by foreign subsidiaries, Global Intangible Low Taxed Income (GILTI), must be included in the gross income of the U.S. shareholder. The 2017 Act also established the Base Erosion and Anti-Abuse Tax (BEAT). The Company is continuing to evaluate the impact of these provisions and has not yet completed a reasonable estimate where we do not have the necessary information available, prepared, and/or analyzed (including computations) as it relates to the impact of the GILTI and BEAT provisions. In addition, Arconic is permitted to make an accounting policy election to either treat taxes due on future inclusions in U.S. taxable income related to GILTI as a current period expense when incurred or factor such amounts into the Company’s deferred tax calculation. Arconic has not yet made this policy decision and will update the GILTI and BEAT impact in accordance with SAB 118. Arconic and its subsidiaries file income tax returns in the U.S. federal jurisdiction and various states and foreign jurisdictions. With a few minor exceptions, Arconic is no longer subject to income tax examinations by tax authorities for years prior to 2006. All U.S. tax years prior to 2017 have been audited by the Internal Revenue Service. Various state and foreign jurisdiction tax authorities are in the process of examining Arconic’s income tax returns for various tax years through 2016. A reconciliation of the beginning and ending amount of unrecognized tax benefits (excluding interest and penalties) was as follows: December 31, 2017 2016 2015 Balance at beginning of year $ 28 $ 18 $ 7 Additions for tax positions of the current year 23 12 — Additions for tax positions of prior years 27 — 14 Reductions for tax positions of prior years — — (2 ) Settlements with tax authorities — (1 ) — Expiration of the statute of limitations (5 ) (1 ) (1 ) Foreign currency translation — — — Balance at end of year $ 73 $ 28 $ 18 For all periods presented, a portion of the balance at end of year pertains to state tax liabilities, which are presented before any offset for federal tax benefits. The effect of unrecognized tax benefits, if recorded, that would impact the annual effective tax rate for 2017 , 2016 and 2015 would be approximately 15% , 6% , and 7% , respectively, of pre-tax book income. Arconic does not anticipate that changes in its unrecognized tax benefits will have a material impact on the Statement of Consolidated Operations during 2018 (see Tax in Note K for a matter for which no reserve has been recognized). It is Arconic’s policy to recognize interest and penalties related to income taxes as a component of the Provision for income taxes on the accompanying Statement of Consolidated Operations. In 2017, Arconic recognized interest of $1 but did not recognize any interest or penalties in 2016 or 2015 . Due to the expiration of the statute of limitations, settlements with tax authorities, and refunded overpayments, Arconic recognized interest income of $2 and $1 in 2017 and 2015 , respectively, but did not recognize any interest income in 2016 . As of December 31, 2017 and 2016 , the amount accrued for the payment of interest and penalties was $2 and $2 , respectively.

Receivables

Receivables	12 Months Ended
	Dec. 31, 2017
Transfers and Servicing [Abstract]
Receivables	Receivables Sale of Receivables Programs Arconic has an arrangement with three financial institutions to sell certain customer receivables without recourse on a revolving basis. The sale of such receivables is completed through the use of a bankruptcy remote special purpose entity, which is a consolidated subsidiary of Arconic. This arrangement provides for minimum funding of $200 up to a maximum of $400 for receivables sold. On March 30, 2012, Arconic initially sold $304 of customer receivables in exchange for $50 in cash and $254 of deferred purchase program under this arrangement. Arconic has received additional net cash funding of $300 for receivables sold ( $2,358 in draws and $2,058 in repayments) since the program’s inception, including $0 ( $600 in draws and $600 in repayments) in 2017 and $100 ( $500 in draws and $400 in repayments) in 2016. As of December 31, 2017 and 2016 , the deferred purchase program receivable was $187 and $83 , respectively, which was included in Other receivables on the accompanying Consolidated Balance Sheet. The deferred purchase program receivable is reduced as collections of the underlying receivables occur; however, as this is a revolving program, the sale of new receivables will result in an increase in the deferred purchase program receivable. The net change in the deferred purchase program receivable was reflected in the (Increase) decrease in receivables line item on the accompanying Statement of Consolidated Cash Flows. This activity is reflected as an operating cash flow because the related customer receivables are the result of an operating activity with an insignificant, short-term interest rate risk. See Note A for additional information on new accounting guidance that will affect the Company during 2018. In 2017 and 2016 , the gross cash outflows and inflows associated with the deferred purchase program receivable were $5,471 and $5,367 , respectively, and $5,340 and $5,406 , respectively. The gross amount of receivables sold and total cash collected under this program since its inception was $35,409 and $34,872 respectively. Arconic services the customer receivables for the financial institutions at market rates; therefore, no servicing asset or liability was recorded. Allowance for Doubtful Accounts The following table details the changes in the allowance for doubtful accounts related to customer receivables and other receivables: Customer receivables Other receivables December 31, 2017 2016 2015 2017 2016 2015 Balance at beginning of year $ 13 $ 8 $ 6 $ 32 $ 34 $ 24 Provision for doubtful accounts 1 7 4 9 6 8 Write off of uncollectible accounts (5 ) (3 ) (2 ) (1 ) (1 ) 2 Recoveries of prior write-offs — (1 ) — (3 ) 1 (1 ) Other (1 ) 2 — (3 ) (8 ) 1 Balance at end of year $ 8 $ 13 $ 8 $ 34 $ 32 $ 34

Interest Cost Components

Interest Cost Components	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Interest Cost Components	Interest Cost Components 2017 2016 2015 Amount charged to expense $ 496 $ 499 $ 473 Amount capitalized 22 32 27 $ 518 $ 531 $ 500

Pension and Other Postretiremen

Pension and Other Postretirement Benefits	12 Months Ended
	Dec. 31, 2017
Retirement Benefits [Abstract]
Pension and Other Postretirement Benefits	Pension and Other Postretirement Benefits Arconic maintains pension plans covering most U.S. employees and certain employees in foreign locations. Pension benefits generally depend on length of service, job grade, and remuneration. Substantially all benefits are paid through pension trusts that are sufficiently funded to ensure that all plans can pay benefits to retirees as they become due. Most salaried and non-bargaining hourly U.S. employees hired after March 1, 2006 participate in a defined contribution plan instead of a defined benefit plan. Arconic also maintains health care and life insurance postretirement benefit plans covering eligible U.S. retired employees and certain retirees from foreign locations. Generally, the medical plans are unfunded and pay a percentage of medical expenses, reduced by deductibles and other coverage. Life benefits are generally provided by insurance contracts. Arconic retains the right, subject to existing agreements, to change or eliminate these benefits. All salaried and certain non-bargaining hourly U.S. employees hired after January 1, 2002 and certain bargaining hourly U.S. employees hired after July 1, 2010 are not eligible for postretirement health care benefits. All salaried and certain hourly U.S. employees that retire on or after April 1, 2008 are not eligible for postretirement life insurance benefits. Effective January 1, 2015, Arconic no longer offers postretirement health care benefits to Medicare-eligible, primarily non-bargaining, U.S. retirees through Company-sponsored plans. Qualifying retirees (hired prior to January 1, 2002), both current and future, may access these benefits in the marketplace by purchasing coverage directly from insurance carriers. Effective August 1, 2016, in preparation for the Separation Transaction, certain U.S. pension and postretirement benefit plans were separated, requiring a remeasurement as of that date. Additionally, one pension plan was required to be remeasured as a result of settlement accounting. Together, these remeasurements resulted in an increase of $845 to Arconic’s pension liability and an increase of $551 (net of tax) to the plans’ unrecognized net actuarial loss (included in Accumulated other comprehensive loss). Effective April 1, 2018, benefit accruals for future service and compensation under all of the Company’s qualified and non-qualified defined benefit pension plans for U.S. salaried and non-bargained hourly employees (the “Pension Plans”) will cease. In connection with this change, effective April 1, 2018, impacted employees will commence receiving an employer contribution of 3% of eligible compensation under the applicable Arconic Retirement Savings Plans, and, for the period from April 1, 2018 through December 31, 2018, an additional transition employer contribution of 3% of eligible compensation. The funded status of all of Arconic’s pension and other postretirement benefit plans are measured as of December 31 each calendar year. Obligations and Funded Status Pension benefits Other postretirement benefits December 31, 2017 2016 2017 2016 Change in benefit obligation Benefit obligation at beginning of year $ 7,026 $ 14,247 $ 980 $ 2,319 Service cost 90 165 7 13 Interest cost 234 435 30 63 Amendments 1 2 — — Actuarial (gains) losses 311 770 1 112 Transfer to Alcoa Corporation — (7,577 ) — (1,340 ) Settlements — (82 ) — — Benefits paid, net of participants’ contributions (425 ) (794 ) (98 ) (197 ) Medicare Part D subsidy receipts — — 7 9 Foreign currency translation impact 122 (140 ) — 1 Benefit obligation at end of year (1) $ 7,359 $ 7,026 $ 927 $ 980 Change in plan assets (1) Fair value of plan assets at beginning of year $ 4,666 $ 10,928 $ — $ — Actual return on plan assets 212 89 — — Employer contributions 310 296 — — Participants’ contributions — 16 — — Benefits paid (404 ) (762 ) — — Administrative expenses (33 ) (65 ) — — Transfer to Alcoa Corporation — (5,610 ) — — Settlements — (82 ) — — Foreign currency translation impact 111 (144 ) — — Fair value of plan assets at end of year (1) $ 4,862 $ 4,666 $ — $ — Funded status* $ (2,497 ) $ (2,360 ) $ (927 ) $ (980 ) Less: Amounts attributed to joint venture partners — — — — Net funded status $ (2,497 ) $ (2,360 ) $ (927 ) $ (980 ) Amounts recognized in the Consolidated Balance Sheet consist of: Noncurrent assets $ 89 $ 6 $ — $ — Current liabilities (22 ) (21 ) (86 ) (91 ) Noncurrent liabilities (2,564 ) (2,345 ) (841 ) (889 ) Net amount recognized $ (2,497 ) $ (2,360 ) $ (927 ) $ (980 ) Amounts recognized in Accumulated Other Comprehensive Loss consist of: Net actuarial loss $ 3,240 $ 2,979 $ 146 $ 150 Prior service cost (benefit) 10 15 (37 ) (45 ) Total, before tax effect 3,250 2,994 109 105 Less: Amounts attributed to joint venture partners — — — — Net amount recognized, before tax effect $ 3,250 $ 2,994 $ 109 $ 105 Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Loss consist of: Net actuarial loss (gain) $ 481 $ (1,992 ) $ 1 $ (224 ) Amortization of accumulated net actuarial loss (220 ) (380 ) (5 ) (24 ) Prior service (benefit) cost — (42 ) — 37 Amortization of prior service (cost) benefit (5 ) (13 ) 8 24 Total, before tax effect 256 (2,427 ) 4 (187 ) Less: Amounts attributed to joint venture partners — 38 — — Net amount recognized, before tax effect $ 256 $ (2,389 ) $ 4 $ (187 ) (1) At December 31, 2017 , the benefit obligation, fair value of plan assets, and funded status for U.S. pension plans were $6,018 , $3,544 , and $(2,474) , respectively. At December 31, 2016 , the benefit obligation, fair value of plan assets, and funded status for U.S. pension plans were $5,707 , $3,495 , and $(2,212) , respectively. Pension Plan Benefit Obligations Pension benefits 2017 2016 The projected benefit obligation and accumulated benefit obligation for all defined benefit pension plans was as follows: Projected benefit obligation $ 7,359 $ 7,026 Accumulated benefit obligation 7,169 6,850 The aggregate projected benefit obligation and fair value of plan assets for pension plans with projected benefit obligations in excess of plan assets was as follows: Projected benefit obligation 6,600 6,995 Fair value of plan assets 4,016 4,629 The aggregate accumulated benefit obligation and fair value of plan assets for pension plans with accumulated benefit obligations in excess of plan assets was as follows: Accumulated benefit obligation 6,422 6,104 Fair value of plan assets 3,998 3,894 Components of Net Periodic Benefit Cost Pension benefits (1) Other postretirement benefits (2) 2017 2016 2015 2017 2016 2015 Service cost $ 90 $ 155 $ 175 $ 7 $ 13 $ 14 Interest cost 234 431 577 30 63 92 Expected return on plan assets (332 ) (677 ) (753 ) — — — Recognized net actuarial loss 220 380 468 5 24 17 Amortization of prior service cost (benefit) 5 13 16 (8 ) (24 ) (37 ) Settlements (3) — 19 16 — — — Curtailments (4) — — 9 — — (4 ) Special termination benefits (5) — 2 16 — — — Net periodic benefit cost (6) $ 217 $ 323 $ 524 $ 34 $ 76 $ 82 Discontinued operations — 122 248 — 41 43 Net amount recognized in Statement of Consolidated Operations $ 217 $ 201 $ 276 $ 34 $ 35 $ 39 Note: the footnotes below include components of Net Periodic Benefit Cost related to Alcoa Corporation through the completion of the Separation Transaction. (1) In 2017 , 2016 and 2015 , net periodic benefit cost for U.S. pension plans was $206 , $261 , and $423 , respectively. (2) In 2017 , 2016 and 2015 , net periodic benefit cost for other postretirement benefits reflects a reduction of $11 , $22 , and $34 , respectively, related to the recognition of the federal subsidy awarded under Medicare Part D. (3) In 2016, settlements were due to workforce reductions (see Note D) and the payment of lump sum benefits and/or purchases of annuity contracts. In 2015, settlements were due to workforce reductions (see Note D) and the payment of lump sum benefits and/or purchases of annuity contracts. (4) In 2015, curtailments were due to elimination of benefits or workforce reductions (see Note D). (5) In 2016 and 2015, special termination benefits were due to workforce reductions (see Note D). (6) Amounts attributed to joint venture partners are not included. Amounts Expected to be Recognized in Net Periodic Benefit Cost Pension benefits Other postretirement benefits 2018 2018 Net actuarial loss recognition 168 9 Prior service cost (benefit) recognition 3 (8 ) Assumptions Weighted average assumptions used to determine benefit obligations for U.S. pension and other postretirement benefit plans were as follows (assumptions for non-U.S. plans did not differ materially): December 31, 2017 2016 Discount rate 3.75 % 4.20 % Rate of compensation increase 3.50 3.50 The discount rate is determined using a Company-specific yield curve model (above-median) developed with the assistance of an external actuary. The cash flows of the plans’ projected benefit obligations are discounted using a single equivalent rate derived from yields on high quality corporate bonds, which represent a broad diversification of issuers in various sectors, including finance and banking, industrials, transportation, and utilities, among others. The yield curve model parallels the plans’ projected cash flows, which have an average duration of 11 years. The underlying cash flows of the bonds included in the model exceed the cash flows needed to satisfy the Company’s plans’ obligations multiple times. The rate of compensation increase is based upon actual experience. For 2018 , the rate of compensation increase will be 3.5% , which approximates the five -year average. Weighted average assumptions used to determine net periodic benefit cost for U.S. pension and other postretirement benefit plans were as follows (assumptions for non-U.S. plans did not differ materially): 2017 2016 2015 Discount rate to calculate service cost* 4.20 % 4.29 % 4.00 % Discount rate to calculate interest cost* 3.60 3.15 4.00 Expected long-term rate of return on plan assets 7.75 7.75 7.75 Rate of compensation increase 3.50 3.50 3.50 * In all periods presented, the respective discount rates were used to determine net periodic benefit cost for most U.S. pension plans for the full annual period. However, the discount rates for a limited number of plans were updated during 2017 , 2016 , and 2015 to reflect the remeasurement of these plans due to new union labor agreements, settlements, and/or curtailments. The updated discount rates used were not significantly different from the discount rates presented. In conjunction with the annual measurement of the funded status of Arconic’s pension and other postretirement benefit plans at December 31, 2015, management elected to change the manner in which the interest cost component of net periodic benefit costs is determined in 2016 and beyond. Previously, the interest component was determined by multiplying the single equivalent rate and the aggregate discounted cash flows of the plans’ projected benefit obligations. Under the new methodology, the interest cost component is determined by aggregating the product of the discounted cash flows of the plans’ projected benefit obligations for each year and an individual spot rate (referred to as the “spot rate” approach). This change resulted in a lower interest cost component of net periodic benefit cost under the new methodology compared to the previous methodology in 2017 and 2016 of $34 and $84 , respectively, for pension plans and $6 and $14 , respectively, for other postretirement benefit plans. Management believes this new methodology, which represents a change in an accounting estimate, is a better measure of the interest cost as each year’s cash flows are specifically linked to the interest rates of bond payments in the same respective year. The expected long-term rate of return on plan assets is generally applied to a five -year market-related value of plan assets (a fair value at the plan measurement date is used for certain non-U.S. plans). The process used by management to develop this assumption is one that relies on a combination of historical asset return information and forward-looking returns by asset class. As it relates to historical asset return information, management focuses on various historical moving averages when developing this assumption. While consideration is given to recent performance and historical returns, the assumption represents a long-term, prospective return. Management also incorporates expected future returns on current and planned asset allocations using information from various external investment managers and consultants, as well as management’s own judgment. For 2017 , 2016 and 2015 , the expected long-term rate of return used by management was based on the prevailing and planned strategic asset allocations, as well as estimates of future returns by asset class. These rates fell within the respective range of the 20 -year moving average of actual performance and the expected future return developed by asset class. In 2015, the decrease of 25 basis points in the expected long-term rate of return was due to a decrease in the 20 -year moving average of actual performance. For 2018 , management anticipates that 7.00% will be the expected long-term rate of return. The decrease of 75 basis points in the expected long-term rate is due to a decrease in the expected return by asset class and the 20-year moving average. Assumed health care cost trend rates for U.S. other postretirement benefit plans were as follows (assumptions for non-U.S. plans did not differ materially): 2017 2016 2015 Health care cost trend rate assumed for next year 5.50 % 5.50 % 5.50 % Rate to which the cost trend rate gradually declines 4.50 % 4.50 % 4.50 % Year that the rate reaches the rate at which it is assumed to remain 2021 2020 2019 The assumed health care cost trend rate is used to measure the expected cost of gross eligible charges covered by Arconic’s other postretirement benefit plans. For 2018 , a 5.5% trend rate will be used, reflecting management’s best estimate of the change in future health care costs covered by the plans. The plans’ actual annual health care cost trend experience over the past three years has ranged from ( 2.2% ) to 9.0% . Management does not believe this three-year range is indicative of expected increases for future health care costs over the long-term. Assumed health care cost trend rates have an effect on the amounts reported for the health care plan. A one-percentage point change in these assumed rates would have the following effects: 1% increase 1% decrease Effect on other postretirement benefit obligations $ 29 $ (28 ) Effect on total of service and interest cost components 1 (1 ) Plan Assets Arconic’s pension plans’ investment policy and weighted average asset allocations at December 31, 2017 and 2016 , by asset class, were as follows: Plan assets at December 31, Asset class Policy range 2017 2016 Equities 20–55% 28 % 30 % Fixed income 25–55% 47 42 Other investments 15–35% 25 28 Total 100 % 100 % The principal objectives underlying the investment of the pension plans’ assets are to ensure that Arconic can properly fund benefit obligations as they become due under a broad range of potential economic and financial scenarios, maximize the long-term investment return with an acceptable level of risk based on such obligations, and broadly diversify investments across and within various asset classes to protect asset values against adverse movements. Specific objectives for long-term investment strategy include reducing the volatility of pension assets relative to pension liabilities and achieving diversification across the balance of the asset portfolio. The use of derivative instruments is permitted where appropriate and necessary for achieving overall investment policy objectives. The investment strategy has used long duration cash bonds and derivative instruments to offset a portion of the interest rate sensitivity of U.S. pension liabilities. Exposure to broad equity risk has been decreased and diversified through investments in discretionary and systematic macro hedge funds, long/short equity hedge funds, high yield bonds, emerging market debt and global and emerging market equities. Investments are further diversified by strategy, asset class, geography, and sector to enhance returns and mitigate downside risk. A large number of external investment managers are used to gain broad exposure to the financial markets and to mitigate manager-concentration risk. Investment practices comply with the requirements of the Employee Retirement Income Security Act of 1974 (ERISA) and other applicable laws and regulations. The following section describes the valuation methodologies used by the trustees to measure the fair value of pension plan assets, including an indication of the level in the fair value hierarchy in which each type of asset is generally classified (see Note U for the definition of fair value and a description of the fair value hierarchy). Equities. These securities consist of: (i) direct investments in the stock of publicly traded U.S. and non-U.S. companies and are valued based on the closing price reported in an active market on which the individual securities are traded (generally classified in Level 1); (ii) the plans’ share of commingled funds that are invested in the stock of publicly traded companies and are valued at the net asset value of shares held at December 31 (included in Level 1); and (iii) direct investments in long/short equity hedge funds and private equity (limited partnerships and venture capital partnerships) and are valued by investment managers based on the most recent financial information available, which typically represents significant unobservable data. Fixed income. These securities consist of: (i) U.S. government debt and are generally valued using quoted prices (included in Level 1); (ii) publicly traded U.S. and non-U.S. fixed interest obligations (principally corporate and sovereign bonds and debentures) and are valued through consultation and evaluation with brokers in the institutional market using quoted prices and other observable market data (included in Level 2); (iii) cash and cash equivalents; and (iv) interest rate swaps and are generally valued using industry standard models with market-based observable inputs. Other investments. These investments include, among others: (i) exchange traded funds, such as gold, and real estate investment trusts and are valued based on the closing price reported in an active market on which the investments are traded (included in Level 1) and (ii) direct investments of discretionary and systematic macro hedge funds and private real estate (includes limited partnerships) and are valued by investment managers based on the most recent financial information available, which typically represents significant unobservable data. The fair value methods described above may not be indicative of net realizable value or reflective of future fair values. Additionally, while Arconic believes the valuation methods used by the plans’ trustees are appropriate and consistent with other market participants, the use of different methodologies or assumptions to determine the fair value of certain financial instruments could result in a different fair value measurement at the reporting date. The following table presents the fair value of pension plan assets classified under the appropriate level of the fair value hierarchy or net asset cost: December 31, 2017 Level 1 Level 2 Net asset value Total Equities: Equity securities $ 379 $ — $ 593 $ 972 Long/short equity hedge funds — — 230 230 Private equity — — 155 155 $ 379 $ — $ 978 $ 1,357 Fixed income: Intermediate and long duration government/credit $ 201 $ 981 $ 779 $ 1,961 Other 164 8 145 317 $ 365 $ 989 $ 924 $ 2,278 Other investments: Real estate $ 85 $ — $ 172 $ 257 Discretionary and systematic macro hedge funds — — 583 583 Other 77 7 275 359 $ 162 $ 7 $ 1,030 $ 1,199 Net plan assets* $ 906 $ 996 $ 2,932 $ 4,834 December 31, 2016 Level 1 Level 2 Net Asset Value Total Equities Equity securities $ 393 $ — $ 431 $ 824 Long/short equity hedge funds — — 406 406 Private equity — — 165 165 $ 393 $ — $ 1,002 $ 1,395 Fixed income: Intermediate and long duration government/credit $ 23 $ 95 $ 655 $ 773 Other 1,060 51 74 1,185 $ 1,083 $ 146 $ 729 $ 1,958 Other investments: Real estate $ 81 $ — $ 185 $ 266 Discretionary and systematic macro hedge funds — — 784 784 Other 65 — 178 243 $ 146 $ — $ 1,147 $ 1,293 Net plan assets** $ 1,622 $ 146 $ 2,878 $ 4,646 * As of December 31, 2017 , the total fair value of pension plans’ assets excludes a net receivable of $28 , which represents assets due from Alcoa Corporation as a result of plan separations and securities sold but not yet settled plus interest and dividends earned on various investments. ** As of December 31, 2016 , the total fair value of pension plans’ assets excludes a net receivable of $20 , which represents assets due from Alcoa Corporation as a result of plan separations and securities sold not yet settled plus interest and dividends earned on various investments. Funding and Cash Flows It is Arconic’s policy to fund amounts for pension plans sufficient to meet the minimum requirements set forth in applicable country benefits laws and tax laws. Periodically, Arconic contributes additional amounts as deemed appropriate. In 2017 and 2016 , cash contributions to Arconic’s pension plans were $310 and $290 . The minimum required contribution to pension plans in 2018 is estimated to be $350 , of which $320 is for U.S. plans. During the third quarter of 2016, the Pension Benefit Guaranty Corporation approved management’s plan to separate the former Alcoa Inc. pension plans between Arconic and Alcoa Corporation in connection with the Separation Transaction. The plan stipulates that Arconic will make cash contributions totaling $150 over a period of 30 months to its two largest pension plans. The payments are expected to be made in increments no less than $50 each over the 30 -month period, with the first payment due no later than six months after the separation date of November 1, 2016. The first payment of $50 was made on April 18, 2017. Benefit payments expected to be paid to pension and other postretirement benefit plans’ participants and expected Medicare Part D subsidy receipts are as follows utilizing the current assumptions outlined above: Year ended December 31, Pension benefits paid Gross Other post- retirement benefits Medicare Part D subsidy receipts Net Other post- retirement benefits 2018 $ 435 $ 90 $ 5 $ 85 2019 440 90 5 85 2020 440 90 5 85 2021 445 90 5 85 2022 450 90 5 85 Thereafter 2,265 335 25 310 $ 4,475 $ 785 $ 50 $ 735 Defined Contribution Plans Arconic sponsors savings and investment plans in various countries, primarily in the United States. Expenses related to these plans were $89 in 2017 , $71 in 2016 , and $83 in 2015 . In the United States, employees may contribute a portion of their compensation to the plans, and Arconic matches a portion of these contributions in equivalent form of the investments elected by the employee.

Other Financial Instruments

Other Financial Instruments	12 Months Ended
	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Other Financial Instruments	Other Financial Instruments Fair Value. Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. The fair value hierarchy distinguishes between (i) market participant assumptions developed based on market data obtained from independent sources (observable inputs) and (ii) an entity’s own assumptions about market participant assumptions developed based on the best information available in the circumstances (unobservable inputs). The fair value hierarchy consists of three broad levels, which gives the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (Level 1) and the lowest priority to unobservable inputs (Level 3). The three levels of the fair value hierarchy are described below: • Level 1—Unadjusted quoted prices in active markets that are accessible at the measurement date for identical, unrestricted assets or liabilities. • Level 2—Inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly, including quoted prices for similar assets or liabilities in active markets; quoted prices for identical or similar assets or liabilities in markets that are not active; inputs other than quoted prices that are observable for the asset or liability (e.g., interest rates); and inputs that are derived principally from or corroborated by observable market data by correlation or other means. • Level 3—Inputs that are both significant to the fair value measurement and unobservable. The carrying values and fair values of Arconic’s financial instruments were as follows: 2017 2016 December 31, Carrying value Fair value Carrying value Fair value Cash and cash equivalents $ 2,150 $ 2,150 $ 1,863 $ 1,863 Restricted cash 4 4 15 15 Derivatives – current asset 61 61 14 14 Noncurrent receivables 20 20 21 21 Derivatives – noncurrent asset 33 33 10 10 Available-for-sale securities 106 106 102 102 Investment in common stock of Alcoa Corporation — — 1,020 1,020 Short-term debt 38 38 40 40 Derivatives – current liability 45 45 5 5 Commercial paper — — — — Derivatives – noncurrent liability 14 14 3 3 Contingent payment related to an acquisition — — 78 78 Long-term debt, less amount due within one year 6,806 7,443 8,044 8,519 The following methods were used to estimate the fair values of financial instruments: Cash and cash equivalents, Restricted cash, Short-term debt, and Commercial paper. The carrying amounts approximate fair value because of the short maturity of the instruments. The fair value amounts for Cash and cash equivalents, Restricted cash, and Commercial paper were classified in Level 1, and Short-term debt was classified in Level 2. Derivatives. The fair value of derivative contracts classified as Level 1 was based on identical unrestricted assets and liabilities. The fair value of derivative contracts classified as Level 2 was based on inputs other than quoted prices that are observable for the asset or liability (e.g. interest rates). Noncurrent receivables. The fair value of noncurrent receivables was based on anticipated cash flows, which approximates carrying value, and was classified in Level 2 of the fair value hierarchy. Available-for-sale securities. The fair value of such securities was based on quoted market prices. These financial instruments consist of exchange-traded fixed income securities, which are carried at fair value and were classified in Level 1 of the fair value hierarchy. Investment in common stock of Alcoa Corporation (see Note C). The fair value was based on the closing stock price of Alcoa Corporation on the New York Stock Exchange at December 31, 2016 multiplied by the number of shares of Alcoa Corporation stock owned by Arconic as of December 31, 2016. This investment was classified in Level 1 of the fair value hierarchy. Contingent payment related to an acquisition (see Note F). The fair value was based on the net present value of expected future cash flows and was classified in Level 3 of the fair value hierarchy. Long-term debt, less amount due within one year. The fair value was based on quoted market prices for public debt and on interest rates that are currently available to Arconic for issuance of debt with similar terms and maturities for non-public debt. The fair value amounts for all Long-term debt were classified in Level 2 of the fair value hierarchy.

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2017
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events Management evaluated all activity of Arconic and concluded that no subsequent events have occurred that would require recognition in the Consolidated Financial Statements or disclosure in the Notes to the Consolidated Financial Statements, except as noted below: In January 2018, the Company announced the freeze of its U.S. defined benefit pension plans for salaried and non-bargained hourly employees, effective April 1, 2018. Benefit accruals for future service and compensation under all of the Company’s qualified and non-qualified defined benefit pension plans for U.S. salaried and non-bargained hourly employees (the “Pension Plans”) will cease. In connection with this change, effective April 1, 2018, impacted employees will commence receiving an employer contribution of 3% of eligible compensation under the Arconic Salaried Retirement Savings Plan, and, for the period from April 1, 2018 through December 31, 2018, an additional transition employer contribution of 3% of eligible compensation. In January 2018, management announced a change in the organizational structure of the Engineered Products and Solutions segment, from four business units to three business units, with a focus on aligning its internal structure to core markets and customers and reducing cost. As a result of this change, goodwill will be reallocated to the three new reporting units and evaluated for impairment during the first quarter of 2018. The Company does not expect any goodwill impairment as a result of the realignment. In February 2018, the Company announced that its Board of Directors authorized a share repurchase program of up to $500 of its outstanding common stock and a $500 early debt reduction. Under the share repurchase program, the Company may repurchase shares from time to time, in amounts, at prices, and at such times as the Company deems appropriate. Repurchases will be subject to market conditions, legal requirements and other considerations. Arconic is not obligated to repurchase any specific number of shares or to do so at any particular time, and the share repurchase program may be suspended, modified or terminated at any time without prior notice. For the early debt reduction, Arconic intends to redeem in March 2018 all of its outstanding 5.72% Notes due in 2019. Beginning in the first quarter of 2018, the Company's primary measure of segment performance will change from Adjusted EBITDA to Operating income, which more closely aligns segment performance with Operating income as presented in the Statement of Consolidated Operations. As part of this change, LIFO and metal price lag will be included in the Operating income of the segments.

Quarterly Data

Quarterly Data	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Quarterly Data	Supplemental Financial Information (unaudited) Quarterly Data (in millions, except per-share amounts) First Second Third Fourth (2) Year 2017 Sales $ 3,192 $ 3,261 $ 3,236 $ 3,271 $ 12,960 Net income (loss) attributable to Arconic $ 322 $ 212 $ 119 $ (727 ) $ (74 ) Earnings (loss) per share attributable to Arconic common shareholders (1) : Basic Net income (loss) per share—basic $ 0.69 $ 0.44 $ 0.23 $ (1.51 ) $ (0.28 ) Diluted Net income (loss) per share—diluted $ 0.65 $ 0.43 $ 0.22 $ (1.51 ) $ (0.28 ) 2016 Sales $ 3,055 $ 3,234 $ 3,138 $ 2,967 $ 12,394 Net income (loss) attributable to Arconic $ 16 $ 135 $ 166 $ (1,258 ) $ (941 ) Earnings (loss) per share attributable to Arconic common shareholders (1) : Basic Continuing operations $ 0.21 $ 0.08 $ 0.11 $ (2.98 ) $ (2.58 ) Discontinued operations (0.21 ) 0.19 0.23 0.07 0.27 Net income (loss) per share—basic $ 0.00 $ 0.27 $ 0.34 $ (2.91 ) $ (2.31 ) Diluted Continuing operations $ 0.21 $ 0.08 $ 0.11 $ (2.98 ) $ (2.58 ) Discontinued operations (0.21 ) 0.19 0.22 0.07 0.27 Net income (loss) per share—basic $ 0.00 $ 0.27 $ 0.33 $ (2.91 ) $ (2.31 ) (1) Per share amounts are calculated independently for each period presented; therefore, the sum of the quarterly per share amounts may not equal the per share amounts for the year. (2) In the fourth quarter of 2017, Arconic recorded an impairment of goodwill related to the forgings and extrusions business of $719 ( $719 pre-tax); a provisional charge of $272 associated with the revaluation of U.S. net deferred tax assets due to a decrease in the U.S. corporate tax rate from 35% to 21% , as well as a one-time transition tax on the non-previously taxed earnings and profits of certain U.S.-owned foreign corporations as of December 31, 2017; a favorable adjustment to the Firth Rixson earn-out liability of $81 ( $81 pre-tax); and a favorable adjustment to a separation-related guarantee liability of $18 ( $25 pre-tax). In the fourth quarter of 2016, as a result of the Separation Transaction, Arconic recorded a charge of $1,267 for valuation allowances on certain deferred tax assets.

Summary of Significant Accoun32

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation. The Consolidated Financial Statements of Arconic Inc. and subsidiaries (“Arconic” or the “Company”) are prepared in conformity with accounting principles generally accepted in the United States of America (GAAP) and require management to make certain judgments, estimates, and assumptions. These may affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the financial statements. They also may affect the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates upon subsequent resolution of identified matters. Certain prior year amounts have been reclassified to conform to the current year presentation. The separation of Alcoa Inc. into two standalone, publicly-traded companies, Arconic Inc. (the new name for Alcoa Inc.) and Alcoa Corporation, became effective on November 1, 2016 (the “Separation Transaction”). The financial results of Alcoa Corporation for all periods prior to the Separation Transaction have been retrospectively reflected in the Statement of Consolidated Operations as discontinued operations and, as such, have been excluded from continuing operations and segment results for all periods presented prior to the Separation Transaction. The cash flows and comprehensive income related to Alcoa Corporation have not been segregated and are included in the Statement of Consolidated Cash Flows and Statement of Consolidated Comprehensive (Loss) Income, respectively, for all periods presented. See Note C for additional information related to the Separation Transaction and discontinued operations.
Principles of Consolidation	Principles of Consolidation. The Consolidated Financial Statements include the accounts of Arconic and companies in which Arconic has a controlling interest. Intercompany transactions have been eliminated. Investments in affiliates in which Arconic cannot exercise significant influence are accounted for on the cost method. Management also evaluates whether an Arconic entity or interest is a variable interest entity and whether Arconic is the primary beneficiary. Consolidation is required if both of these criteria are met. Arconic does not have any variable interest entities requiring consolidation.
Related Party Transactions	Related Party Transactions. Arconic buys products from and provides services to Alcoa Corporation following the separation at negotiated prices between the parties. These transactions were not material to the financial position or results of operations of Arconic for all periods presented. Effective May 2017, upon disposition of the remaining common stock that Arconic held in Alcoa Corporation, they are no longer deemed a related party.
Cash Equivalents	Cash Equivalents. Cash equivalents are highly liquid investments purchased with an original maturity of three months or less.
Inventory Valuation	Inventory Valuation. Inventories are carried at the lower of cost and net realizable value, with cost for approximately half of U.S. inventories determined under the last-in, first-out (LIFO) method. The cost of other inventories is determined under a combination of the first-in, first-out (FIFO) and average-cost methods.
Properties, Plants, and Equipment	Properties, Plants, and Equipment. Properties, plants, and equipment are recorded at cost. Depreciation is recorded principally on the straight-line method at rates based on the estimated useful lives of the assets. The following table details the weighted-average useful lives of structures and machinery and equipment by reporting segment (numbers in years): Segment Structures Machinery and equipment Engineered Products and Solutions 29 17 Global Rolled Products 31 21 Transportation and Construction Solutions 27 18 Gains or losses from the sale of assets are generally recorded in Other income, net (see policy below for assets classified as held for sale and discontinued operations). Repairs and maintenance are charged to expense as incurred. Interest related to the construction of qualifying assets is capitalized as part of the construction costs. Properties, plants, and equipment are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of such assets (asset group) may not be recoverable. Recoverability of assets is determined by comparing the estimated undiscounted net cash flows of the operations related to the assets (asset group) to their carrying amount. An impairment loss would be recognized when the carrying amount of the assets (asset group) exceeds the estimated undiscounted net cash flows. The amount of the impairment loss to be recorded is calculated as the excess of the carrying value of the assets (asset group) over their fair value, with fair value determined using the best information available, which generally is a discounted cash flow (DCF) model. The determination of what constitutes an asset group, the associated estimated undiscounted net cash flows, and the estimated useful lives of assets also require significant judgments.
Goodwill and Other Intangible Assets	Goodwill. Goodwill is not amortized; instead, it is reviewed for impairment annually (in the fourth quarter) or more frequently if indicators of impairment exist or if a decision is made to sell or realign a business. A significant amount of judgment is involved in determining if an indicator of impairment has occurred. Such indicators may include deterioration in general economic conditions, negative developments in equity and credit markets, adverse changes in the markets in which an entity operates, increases in input costs that have a negative effect on earnings and cash flows, or a trend of negative or declining cash flows over multiple periods, among others. The fair value that could be realized in an actual transaction may differ from that used to evaluate the impairment of goodwill. Goodwill is allocated among and evaluated for impairment at the reporting unit level, which is defined as an operating segment or one level below an operating segment. Arconic has eight reporting units, of which four are included in the Engineered Products and Solutions segment, three are included in the Transportation and Construction Solutions segment, and the remaining reporting unit is the Global Rolled Products segment. More than 85% of Arconic’s total goodwill at December 31, 2017 is allocated to two reporting units as follows: Arconic Fastening Systems and Rings (AFSR) ( $2,221 ) and Arconic Power and Propulsion (APP) ( $1,686 ) businesses, both of which are included in the Engineered Products and Solutions segment. These amounts include an allocation of Corporate’s goodwill. In reviewing goodwill for impairment, an entity has the option to first assess qualitative factors to determine whether the existence of events or circumstances leads to a determination that it is more likely than not (greater than 50% ) that the estimated fair value of a reporting unit is less than its carrying amount. If an entity elects to perform a qualitative assessment and determines that an impairment is more likely than not, the entity is then required to perform the quantitative impairment test (described below), otherwise no further analysis is required. An entity also may elect not to perform the qualitative assessment and, instead, proceed directly to the quantitative impairment test. The ultimate outcome of the goodwill impairment review for a reporting unit should be the same whether an entity chooses to perform the qualitative assessment or proceeds directly to the quantitative impairment test. Arconic determines annually, based on facts and circumstances, which of its reporting units will be subject to the qualitative assessment. For those reporting units where a qualitative assessment is either not performed or for which the conclusion is that an impairment is more likely than not, a quantitative impairment test will be performed. Arconic’s policy is that a quantitative impairment test be performed for each reporting unit at least once during every three -year period. Under the qualitative assessment, various events and circumstances (or factors) that would affect the estimated fair value of a reporting unit are identified (similar to impairment indicators above). These factors are then classified by the type of impact they would have on the estimated fair value using positive, neutral, and adverse categories based on current business conditions. Additionally, an assessment of the level of impact that a particular factor would have on the estimated fair value is determined using high, medium, and low weighting. Furthermore, management considers the results of the most recent quantitative impairment test completed for a reporting unit and compares the weighted average cost of capital (WACC) between the current and prior years for each reporting unit. During the 2017 annual review of goodwill, management performed the qualitative assessment for one reporting unit, Arconic Wheel and Transportation Products (within the Transportation and Construction Solutions segment). Management concluded that it was not more likely than not that the estimated fair value of the reporting unit was less than its carrying value. As such, no further analysis was required. Under the quantitative impairment test, the evaluation of impairment involves comparing the current fair value of each reporting unit to its carrying value, including goodwill. Arconic uses a discounted cash flow model (DCF) to estimate the current fair value of its reporting units when testing for impairment, as management believes forecasted cash flows are the best indicator of such fair value. A number of significant assumptions and estimates are involved in the application of the DCF model to forecast operating cash flows, including markets and market share, sales volumes and prices, production costs, tax rates, capital spending, discount rate, and working capital changes. Most of these assumptions vary significantly among the reporting units. Cash flow forecasts are generally based on approved business unit operating plans for the early years and historical relationships in later years. The WACC rate for the individual reporting units is estimated with the assistance of valuation experts. Arconic would recognize an impairment charge for the amount by which the carrying amount exceeds the reporting unit’s fair value without exceeding the total amount of goodwill allocated to that reporting unit. During the 2017 annual review of goodwill, management proceeded directly to the quantitative impairment test for six reporting units as follows: AFSR, APP, Arconic Titanium and Engineered Products (ATEP), and Arconic Forgings and Extrusions (AFE), which are all included in the Engineered Products and Solutions segment, Global Rolled Products, and Building and Construction Systems, which is included in the Transportation and Construction Solutions segment. The estimated fair value for five of the six reporting units exceeded its respective carrying value, resulting in no impairment. However, the estimated fair value of AFE was lower than its carrying value. As such, in the fourth quarter of 2017, Arconic recorded an impairment for the full amount of goodwill in the AFE reporting unit of $719 . The decrease in the AFE fair value was primarily due to unfavorable performance that is impacting operating margins and a higher discount rate due to an increase in the risk-free rate of return, while the carrying value increased compared to prior year. Goodwill impairment tests in 2016 and 2015 indicated that goodwill was not impaired for any of the Company’s reporting units, except for the soft alloy extrusion business in Brazil which is included in the Transportation and Construction Solutions segment. In the fourth quarter of 2015, for the soft alloy extrusion business in Brazil, the estimated fair value as determined by the DCF model was lower than the associated carrying value of its reporting unit’s goodwill. As a result, management determined that the implied fair value of the reporting unit’s goodwill was zero . Arconic recorded a goodwill impairment of $25 in 2015. The impairment of goodwill resulted from headwinds from the downturn in the Brazilian economy and the continued erosion of gross margin despite the execution of cost reduction strategies. As a result of the goodwill impairment, there is no goodwill remaining for the reporting unit. Other Intangible Assets. Intangible assets with indefinite useful lives are not amortized while intangible assets with finite useful lives are amortized generally on a straight-line basis over the periods benefited. The following table details the weighted-average useful lives of software and other intangible assets by reporting segment (numbers in years):
Revenue Recognition	Revenue Recognition. Arconic recognizes revenues when title, ownership, and risk of loss pass to the customer, all of which occurs upon shipment or delivery of the product and is based on the applicable shipping terms. The shipping terms vary across all businesses and depend on the product, the country of origin, and the type of transportation (truck, train, or vessel). In certain circumstances, Arconic receives advanced payments from its customers for product to be delivered in future periods. These advanced payments are recorded as deferred revenue until the product is delivered and title and risk of loss have passed to the customer in accordance with the terms of the contract. Deferred revenue is included in Other current liabilities and Other noncurrent liabilities and deferred credits on the accompanying Consolidated Balance Sheet.
Environmental Matters	Environmental Matters. Expenditures for current operations are expensed or capitalized, as appropriate. Expenditures relating to existing conditions caused by past operations, which will not contribute to future revenues, are expensed. Liabilities are recorded when remediation costs are probable and can be reasonably estimated. The liability may include costs such as site investigations, consultant fees, feasibility studies, outside contractors, and monitoring expenses. Estimates are generally not discounted or reduced by potential claims for recovery. Claims for recovery are recognized when probable and as agreements are reached with third parties. The estimates also include costs related to other potentially responsible parties to the extent that Arconic has reason to believe such parties will not fully pay their proportionate share. The liability is continuously reviewed and adjusted to reflect current remediation progress, prospective estimates of required activity, and other factors that may be relevant, including changes in technology or regulations.
Litigation Matters	Litigation Matters. For asserted claims and assessments, liabilities are recorded when an unfavorable outcome of a matter is deemed to be probable and the loss is reasonably estimable. Management determines the likelihood of an unfavorable outcome based on many factors such as the nature of the matter, available defenses and case strategy, progress of the matter, views and opinions of legal counsel and other advisors, applicability and success of appeals processes, and the outcome of similar historical matters, among others. Once an unfavorable outcome is deemed probable, management weighs the probability of estimated losses, and the most reasonable loss estimate is recorded. If an unfavorable outcome of a matter is deemed to be reasonably possible, then the matter is disclosed and no liability is recorded. With respect to unasserted claims or assessments, management must first determine that the probability that an assertion will be made is likely, then, a determination as to the likelihood of an unfavorable outcome and the ability to reasonably estimate the potential loss is made. Legal matters are reviewed on a continuous basis to determine if there has been a change in management’s judgment regarding the likelihood of an unfavorable outcome or the estimate of a potential loss.
Income Taxes	Income Taxes. The provision for income taxes is determined using the asset and liability approach of accounting for income taxes. Under this approach, the provision for income taxes represents income taxes paid or payable (or received or receivable) for the current year plus the change in deferred taxes during the year. Deferred taxes represent the future tax consequences expected to occur when the reported amounts of assets and liabilities are recovered or paid, and result from differences between the financial and tax bases of Arconic’s assets and liabilities and are adjusted for changes in tax rates and tax laws when enacted. Valuation allowances are recorded to reduce deferred tax assets when it is more likely than not that a tax benefit will not be realized. In evaluating the need for a valuation allowance, management considers all potential sources of taxable income, including income available in carryback periods, future reversals of taxable temporary differences, projections of taxable income, and income from tax planning strategies, as well as all available positive and negative evidence. Positive evidence includes factors such as a history of profitable operations, projections of future profitability within the carryforward period, including from tax planning strategies, and Arconic’s experience with similar operations. Existing favorable contracts and the ability to sell products into established markets are additional positive evidence. Negative evidence includes items such as cumulative losses, projections of future losses, or carryforward periods that are not long enough to allow for the utilization of a deferred tax asset based on existing projections of income. Deferred tax assets for which no valuation allowance is recorded may not be realized upon changes in facts and circumstances, resulting in a future charge to establish a valuation allowance. Existing valuation allowances are re-examined under the same standards of positive and negative evidence. If it is determined that it is more likely than not that a deferred tax asset will be realized, the appropriate amount of the valuation allowance, if any, is released. Deferred tax assets and liabilities are also re-measured to reflect changes in underlying tax rates due to law changes and the granting and lapse of tax holidays. Tax benefits related to uncertain tax positions taken or expected to be taken on a tax return are recorded when such benefits meet a more likely than not threshold. Otherwise, these tax benefits are recorded when a tax position has been effectively settled, which means that the statute of limitations has expired or the appropriate taxing authority has completed their examination even though the statute of limitations remains open. Interest and penalties related to uncertain tax positions are recognized as part of the provision for income taxes and are accrued beginning in the period that such interest and penalties would be applicable under relevant tax law until such time that the related tax benefits are recognized.
Stock-based Compensation	Stock-based Compensation. Arconic recognizes compensation expense for employee equity grants using the non-substantive vesting period approach, in which the expense is recognized ratably over the requisite service period based on the grant date fair value. Forfeitures are accounted for as they occur. The fair value of new stock options is estimated on the date of grant using a lattice-pricing model. The fair value of performance awards containing a market condition is valued using a Monte Carlo valuation model. Determining the fair value at the grant date requires judgment, including estimates for the average risk-free interest rate, dividend yield, volatility, and exercise behavior. These assumptions may differ significantly between grant dates because of changes in the actual results of these inputs that occur over time. Most plan participants can choose whether to receive their award in the form of stock options, stock awards, or a combination of both. This choice is made before the grant is issued and is irrevocable.
Foreign Currency	Foreign Currency. The local currency is the functional currency for Arconic’s significant operations outside the United States, except for certain operations in Canada and Russia, where the U.S. dollar is used as the functional currency. The determination of the functional currency for Arconic’s operations is made based on the appropriate economic and management indicators.
Acquisitions	Acquisitions. Arconic’s business acquisitions are accounted for using the acquisition method. The purchase price is allocated to the assets acquired and liabilities assumed based on their estimated fair values. Any excess purchase price over the fair value of the net assets acquired is recorded as goodwill. For all acquisitions, operating results are included in the Statement of Consolidated Operations from the date of the acquisition.
Discontinued Operations and Assets Held For Sale	Discontinued Operations and Assets Held For Sale. For those businesses where management has committed to a plan to divest, each business is valued at the lower of its carrying amount or estimated fair value less cost to sell. If the carrying amount of the business exceeds its estimated fair value, an impairment loss is recognized. Fair value is estimated using accepted valuation techniques such as a DCF model, valuations performed by third parties, earnings multiples, or indicative bids, when available. A number of significant estimates and assumptions are involved in the application of these techniques, including the forecasting of markets and market share, sales volumes and prices, costs and expenses, and multiple other factors. Management considers historical experience and all available information at the time the estimates are made; however, the fair value that is ultimately realized upon the divestiture of a business may differ from the estimated fair value reflected in the Consolidated Financial Statements. Depreciation and amortization expense is not recorded on assets of a business to be divested once they are classified as held for sale. Businesses to be divested are generally classified in the Consolidated Financial Statements as either discontinued operations or held for sale. For businesses classified as discontinued operations, the balance sheet amounts and results of operations are reclassified from their historical presentation to assets and liabilities of discontinued operations on the Consolidated Balance Sheet and to discontinued operations on the Statement of Consolidated Operations, respectively, for all periods presented. The gains or losses associated with these divested businesses are recorded in discontinued operations on the Statement of Consolidated Operations. The Statement of Consolidated Cash Flows is not required to be reclassified for discontinued operations for any period. Segment information does not include the assets or operating results of businesses classified as discontinued operations for all periods presented. These businesses are expected to be disposed of within one year . For businesses classified as held for sale that do not qualify for discontinued operations treatment, the balance sheet and cash flow amounts are reclassified from their historical presentation to assets and liabilities of operations held for sale for all periods presented. The results of operations continue to be reported in continuing operations. The gains or losses associated with these divested businesses are recorded in Restructuring and other charges on the Statement of Consolidated Operations. The segment information includes the assets and operating results of businesses classified as held for sale for all periods presented.
Recently Adopted and Issued Accounting Guidance	Recently Adopted Accounting Guidance. On January 1, 2017, Arconic adopted changes issued by the Financial Accounting Standards Board (“FASB”) to employee share-based payment accounting. Previously, an entity determined for each share-based payment award whether the difference between the deduction for tax purposes and the compensation cost recognized for financial reporting purposes resulted in either an excess tax benefit or a tax deficiency. Excess tax benefits were recognized in additional paid-in capital; tax deficiencies were recognized either as an offset to accumulated excess tax benefits, if any, or in the income statement. Excess tax benefits were not recognized until the deduction reduced taxes payable. The changes require all excess tax benefits and tax deficiencies related to share-based payment awards to be recognized as income tax expense or benefit in the Statement of Consolidated Operations. The tax effects of exercised or vested awards should be treated as discrete items in the reporting period in which they occur. An entity also should recognize excess tax benefits regardless of whether the benefit reduces taxes payable in the current period. In addition, the presentation of excess tax benefits related to share-based payment awards in the statement of cash flows changed. Previously, excess tax benefits were separated from other income tax cash flows and classified as a financing activity. The changes require excess tax benefits to be classified along with other income tax cash flows as an operating activity. Also, the changes require cash paid by an employer when directly withholding shares for tax-withholding purposes to be classified as a financing activity. Further, for a share-based award to qualify for equity classification it previously could not be partially settled in cash in-excess of the employer’s minimum statutory withholding requirements. The changes permit equity classification of share-based awards for withholdings up to the maximum statutory tax rates in applicable jurisdictions. The prospective transition method was utilized for excess tax benefits in the Statement of Consolidated Cash Flows. Management determined that the adoption of this guidance did not have a material impact on the Consolidated Financial Statements. On January 1, 2017, Arconic adopted changes issued by the FASB eliminating the requirement for an investor to adjust an equity method investment, results of operations, and retained earnings retroactively on a step-by-step basis as if the equity method had been in effect during all previous periods that the investment had been held as a result of an increase in the level of ownership interest or degree of influence. In addition, an entity that has an available-for-sale equity security that becomes qualified for the equity method of accounting must recognize through earnings the unrealized holding gain or loss in accumulated other comprehensive income at the date the investment becomes qualified for use of the equity method. Management determined that the adoption of this guidance had no impact on the Consolidated Financial Statements. On January 1, 2017, Arconic adopted changes issued by the FASB to derivative instruments designated as hedging instruments. These changes clarify that a change in the counterparty to a derivative instrument that has been designated as a hedging instrument does not, in and of itself, require dedesignation of that hedging relationship provided that all other hedge accounting criteria continue to be met. Management determined that the adoption of this guidance did not have a material impact on the Consolidated Financial Statements. On January 1, 2017, Arconic adopted changes issued by the FASB to the accounting for Intra-Entity transactions, other than inventory. Previously, no immediate tax impact was recognized in the consolidated financial statements as a result of intra-entity transfers of assets. The previous standard precluded an entity from reflecting a tax benefit or expense from an intra-entity transfer between entities that file separate tax returns, whether or not such entities were in different tax jurisdictions, until the asset was sold to a third party or otherwise recovered. The previous standard also prohibited recognition by the buyer of a deferred tax asset for the temporary difference arising from the excess of the buyer’s tax basis over the cost to the seller. The changes require the current and deferred income tax consequences of the intra-entity transfer to be recorded when the transaction occurs. The exception to defer the tax consequences of inventory transactions is maintained. Management determined that the adoption of this guidance did not have a material impact on the Consolidated Financial Statements. On January 1, 2017, Arconic adopted changes issued by the FASB to the subsequent measurement of goodwill by eliminating step 2 from the goodwill impairment test, which previously required measurement of any goodwill impairment loss by comparing the implied fair value of a reporting unit’s goodwill with the carrying amount of that goodwill. An entity will perform its annual, or interim, goodwill impairment test by comparing the fair value of a reporting unit with its carrying amount and recognize an impairment charge for the amount by which the carrying amount exceeds the reporting unit’s fair value without exceeding the total amount of goodwill allocated to that reporting unit. Arconic applied this new guidance on a prospective basis. See Goodwill policy above for further details. On January 1, 2017, Arconic adopted changes issued by the FASB which narrow the definition of a business and require an entity to evaluate if substantially all of the fair value of the gross assets acquired is concentrated in a single identifiable asset or a group of similar identifiable assets, which would not constitute the acquisition of a business. The guidance also requires a business to include at least one substantive process and narrows the definition of outputs. Arconic applied this new guidance on a prospective basis. Management determined that the adoption of this guidance had no impact on the Consolidated Financial Statements. On January 1, 2017, Arconic adopted changes issued by the FASB to the subsequent measurement of inventory. Previously, an entity was required to measure its inventory at the lower of cost or market, whereby market can be replacement cost, net realizable value, or net realizable value less an approximately normal profit margin. The changes required that inventory be measured at the lower of cost and net realizable value, thereby eliminating the use of the other two market methodologies. Net realizable value is defined as the estimated selling prices in the ordinary course of business less reasonably predictable costs of completion, disposal, and transportation. These changes did not apply to inventories measured using LIFO (last-in, first-out) or the retail inventory method. Arconic applies the net realizable value market option to measure non-LIFO inventories at the lower of cost or market. Management determined that the adoption of this guidance did not have a material impact on the Consolidated Financial Statements. Recently Issued Accounting Guidance. In May 2014, the FASB issued changes to the recognition of revenue from contracts with customers. These changes created a comprehensive framework for all entities in all industries to apply in the determination of when to recognize revenue and, therefore, supersede virtually all existing revenue recognition requirements and guidance. This framework is expected to result in less complex guidance in application while providing a consistent and comparable methodology for revenue recognition. The core principle of the guidance is that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. To achieve this principle, an entity should apply the following steps: (i) identify the contract(s) with a customer, (ii) identify the performance obligations in the contract(s), (iii) determine the transaction price, (iv) allocate the transaction price to the performance obligations in the contract(s), and (v) recognize revenue when, or as, the entity satisfies a performance obligation. In August 2015, the FASB deferred the effective date of the new guidance by one year, making these changes effective for Arconic on January 1, 2018. Arconic will adopt the new guidance using the modified retrospective transition approach, reflecting the cumulative effect of initially applying the new standard to revenue recognition in the first quarter of 2018. The Company had formed a project assessment and adoption team that reviewed contract terms to assess the impact of adopting the new guidance on the Consolidated Financial Statements. While the Company generally recognizes revenue at a point in time upon delivery and transfer of title and risk of loss for most arrangements, based on the contract reviews performed, certain contracts within the Engineered Products and Solutions segment were identified as potentially moving to over time revenue recognition. The Company modified certain contract terms in conjunction with its customers to remain at point-in-time revenue recognition. These modifications will not result in significant changes to revenue, business practices or controls. Management has determined that the adoption of this guidance will not have a material impact on the Consolidated Financial Statements. The Company is in the process of identifying appropriate changes to its business processes and controls, as well as preparing for revisions to accounting policies and expanded disclosures related to revenue recognition in the notes to the Consolidated Financial Statements. In January 2016, the FASB issued changes to equity investments. These changes require equity investments (except those accounted for under the equity method of accounting or those that result in consolidation of the investee) to be measured at fair value with changes in fair value recognized in net income. However, an entity may choose to measure equity investments that do not have readily determinable fair values using the measurement alternative of cost minus impairment, if any, plus or minus changes resulting from observable price changes in orderly transactions for the identical or similar investment of the same issuer. Also, the impairment assessment of equity investments without readily determinable fair values has been simplified by requiring a qualitative assessment to identify impairment. Also, the new guidance will require changes in fair value of equity securities to be recognized immediately as a component of net income instead of being reported in accumulated other comprehensive loss until the gain (loss) is realized. These changes became effective for Arconic on January 1, 2018 and have been applied on a prospective basis. Arconic elected the measurement alternative for its equity investments that do not have readily determinable fair values. Management determined that the adoption of this guidance will not have a material impact on the Consolidated Financial Statements. In February 2016, the FASB issued changes to the accounting and presentation of leases. These changes require lessees to recognize a right of use asset and lease liability on the balance sheet for all leases with terms longer than 12 months. For leases with a term of 12 months or less, a lessee is permitted to make an accounting policy election by class of underlying asset not to recognize a right of use asset and lease liability. Additionally, when measuring assets and liabilities arising from a lease, optional payments should be included only if the lessee is reasonably certain to exercise an option to extend the lease, exercise a purchase option, or not exercise an option to terminate the lease. These changes become effective for Arconic on January 1, 2019. Arconic’s current operating lease portfolio is primarily comprised of land and buildings, plant equipment, vehicles, and computer equipment. A cross-functional implementation team is in process of determining the scope of arrangements that will be subject to this standard as well as assessing the impact to the Company’s systems, processes and internal controls. Management is evaluating the impact of these changes on the Consolidated Financial Statements, which will require right of use assets and lease liabilities be recorded in the consolidated balance sheet for operating leases. Therefore, an estimate of the impact is not currently determinable. However, the adoption is not expected to have a material impact on the Statement of Consolidated Operations. In June 2016, the FASB added a new impairment model (known as the current expected credit loss (CECL) model) that is based on expected losses rather than incurred losses. Under the new guidance, an entity recognizes as an allowance its estimate of expected credit losses. The CECL model applies to most debt instruments, trade receivables, lease receivables, financial guarantee contracts, and other loan commitments. The CECL model does not have a minimum threshold for recognition of impairment losses and entities will need to measure expected credit losses on assets that have a low risk of loss. These changes become effective for Arconic on January 1, 2020. Management is currently evaluating the potential impact of these changes on the Consolidated Financial Statements. In August 2016, the FASB issued changes to the classification of certain cash receipts and cash payments within the statement of cash flows. The guidance identifies eight specific cash flow items and the sections where they must be presented within the statement of cash flows. These changes became effective for Arconic on January 1, 2018 and will be applied retrospectively. As of result of the adoption, Arconic will reclassify cash received related to beneficial interest in previously transferred trade accounts receivables from operating activities to investing activities in the Statement of Consolidated Cash Flows. This reclassification is expected to have a material impact on the Statement of Consolidated Cash Flows, but does not reflect a change in our underlying business or activities. Additionally, Arconic will reclassify cash paid for debt prepayments including extinguishment costs from operating activities to financing activities in the Statement of Consolidated Cash Flows. In November 2016, the FASB issued changes to the classification of cash and cash equivalents within the statement of cash flow. Restricted cash and restricted cash equivalents will be included within the cash and cash equivalents line on the cash flow statement and a reconciliation must be prepared to the statement of financial position. Transfers between restricted cash and restricted cash equivalents and cash and cash equivalents will no longer be presented as cash flow activities in the statement of cash flows and for material balances of restricted cash and restricted cash equivalents an entity must disclose information regarding the nature of the restrictions. These changes became effective for Arconic on January 1, 2018 and will be applied retrospectively. Management has determined that the adoption of this guidance will not have a material impact on the Statement of Consolidated Cash Flows. In March 2017, the FASB issued changes to shorten the amortization period for certain callable debt securities held at a premium. Specifically, the amendments require the premium to be amortized to the earliest call date. The amendments do not require an accounting change for securities held at a discount; the discount continues to be amortized to maturity. These changes become effective for Arconic on January 1, 2019 and early adoption is permitted. Management has determined that the adoption of this guidance will not have a material impact on the Consolidated Financial Statements. In March 2017, the FASB issued changes to the presentation of net periodic pension cost and net periodic postretirement benefit cost. The new guidance requires registrants to present the service cost component of net periodic benefit cost in the same income statement line item or items as other employee compensation costs arising from services rendered during the period. Also, only the service cost component will be eligible for asset capitalization. Registrants will present the other components of net periodic benefit cost separately from the service cost component; and, the line item or items used in the income statement to present the other components of net periodic benefit cost must be disclosed. These changes became effective for Arconic on January 1, 2018 and will be adopted retrospectively for the presentation of the service cost component and the other components of net periodic benefit cost in the income statement, and prospectively for the asset capitalization of the service cost component of net periodic benefit cost. The Company currently records non-service related net periodic pension cost and net periodic postretirement benefit cost within Cost of goods sold, Selling, general, administrative and other expenses and Research and development expenses and upon the adoption of this standard will be recorded separately from service cost in the Other income, net line item in the Statement of Consolidated Operations. The impact of the retrospective adoption of this guidance will be an increase to consolidated Operating income of approximately $154 and $135 while there will be no impact to consolidated Net loss for the years ended December 31, 2017 and 2016, respectively. The prospective adoption of the asset capitalization of only the service cost component will have an impact of approximately $20 in the first quarter of 2018 Statement of Consolidated Operations. In May 2017, the FASB issued clarification to guidance on the modification accounting criteria for share-based payment awards. The new guidance requires registrants to apply modification accounting unless three specific criteria are met. The three criteria are 1) the fair value of the award is the same before and after the modification, 2) the vesting conditions are the same before and after the modification and 3) the classification as a debt or equity award is the same before and after the modification. These changes became effective for Arconic on January 1, 2018 and are to be applied prospectively to new awards granted after adoption. Management determined that the adoption of this guidance will not have a material impact on the Consolidated Financial Statements. In August 2017, the FASB issued guidance that will make more financial and nonfinancial hedging strategies eligible for hedge accounting. It also amends the presentation and disclosure requirements and changes how companies assess effectiveness. It is intended to more closely align hedge accounting with companies’ risk management strategies, simplify the application of hedge accounting, and increase transparency as to the scope and results of hedging programs. These changes become effective for Arconic on January 1, 2019. For cash flow and net investment hedges existing at the date of adoption, Arconic will apply a cumulative-effect adjustment related to eliminating the separate measurement of ineffectiveness to accumulated other comprehensive income with a corresponding adjustment to the opening balance of retained earnings as of the beginning of the fiscal year in which the amendment is adopted. The amended presentation and disclosure guidance is required only prospectively. Management is currently evaluating the potential impact of this guidance on the Consolidated Financial Statements. In February 2018, the FASB issued guidance that allows a reclassification from Accumulated other comprehensive loss to Accumulated deficit for stranded tax effects resulting from the Tax Cuts and Jobs Act enacted on December 22, 2017. These changes become effective for Arconic on January 1, 2019. Management is currently evaluating the potential impact of this guidance on the Consolidated Financial Statements.

Summary of Significant Accoun33

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Weighted-Average Useful Lives of Structures and Machinery and Equipment	The following table details the weighted-average useful lives of structures and machinery and equipment by reporting segment (numbers in years): Segment Structures Machinery and equipment Engineered Products and Solutions 29 17 Global Rolled Products 31 21 Transportation and Construction Solutions 27 18
Weighted-Average Useful Lives of Software and Other Intangible Assets	The following table details the weighted-average useful lives of software and other intangible assets by reporting segment (numbers in years): Segment Software Other intangible assets Engineered Products and Solutions 6 34 Global Rolled Products 6 9 Transportation and Construction Solutions 5 16

Accumulated Other Comprehensi34

Accumulated Other Comprehensive Loss (Tables)	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Summary of Changes in Accumulated Other Comprehensive (Loss) by Component	The following table details the activity of the four components that comprise Accumulated other comprehensive loss for both Arconic’s shareholders and noncontrolling interests: Arconic Noncontrolling Interests 2017 2016 2015 2017 2016 2015 Pension and other postretirement benefits (U) Balance at beginning of period $ (2,010 ) $ (3,611 ) $ (3,601 ) $ — $ (56 ) $ (64 ) Other comprehensive (loss) income: Unrecognized net actuarial loss and prior service cost/benefit (466 ) (1,112 ) (478 ) — (9 ) 5 Tax benefit (expense) 102 380 170 — 3 (1 ) Total Other comprehensive (loss) income before reclassifications, net of tax (364 ) (732 ) (308 ) — (6 ) 4 Amortization of net actuarial loss and prior service cost/benefit (1) 222 389 458 — 4 6 Tax expense (2) (78 ) (136 ) (160 ) — (1 ) (2 ) Total amount reclassified from Accumulated other comprehensive loss, net of tax (8) 144 253 298 — 3 4 Total Other comprehensive (loss) income (220 ) (479 ) (10 ) — (3 ) 8 Transfer to Alcoa Corporation — 2,080 — — 59 — Balance at end of period $ (2,230 ) $ (2,010 ) $ (3,611 ) $ — $ — $ (56 ) Foreign currency translation Balance at beginning of period $ (689 ) $ (2,412 ) $ (846 ) $ (2 ) $ (780 ) $ (351 ) Other comprehensive income (loss) (3) 252 268 (1,566 ) 2 182 (429 ) Transfer to Alcoa Corporation — 1,455 — — 596 — Balance at end of period $ (437 ) $ (689 ) $ (2,412 ) $ — $ (2 ) $ (780 ) Available-for-sale securities Balance at beginning of period $ 132 $ (5 ) $ — $ — $ — $ — Other comprehensive (loss) income (4) (134 ) 137 (5 ) — — — Transfer to Alcoa Corporation — — — — — — Balance at end of period $ (2 ) $ 132 $ (5 ) $ — $ — $ — Cash flow hedges Balance at beginning of period $ (1 ) $ 597 $ (230 ) — $ (3 ) $ (2 ) Other comprehensive income (loss): Net change from periodic revaluations 37 (843 ) 1,138 — 36 (1 ) Tax (expense) benefit (9 ) 252 (340 ) — (10 ) — Total Other comprehensive income (loss) before reclassifications, net of tax 28 (591 ) 798 — 26 (1 ) Net amount reclassified to earnings: Aluminum contracts (5) (2 ) 1 21 — — — Energy contracts (6) — (49 ) 6 — (34 ) — Foreign exchange contracts (5) — — 5 — — — Interest rate contracts (7) — 9 1 — 5 — Nickel contracts (6) (1 ) 1 2 — — — Sub-total (3 ) (38 ) 35 — (29 ) — Tax benefit (expense) (2) 1 12 (6 ) — 8 — Total amount reclassified from Accumulated other comprehensive loss, net of tax (8) (2 ) (26 ) 29 — (21 ) — Total Other comprehensive income (loss) 26 (617 ) 827 — 5 (1 ) Transfer to Alcoa Corporation — 19 — — (2 ) — Balance at end of period $ 25 $ (1 ) $ 597 $ — $ — $ (3 ) (1) These amounts were included in the computation of net periodic benefit cost for pension and other postretirement benefits (see Note T). (2) These amounts were included in Provision for income taxes on the accompanying Statement of Consolidated Operations. (3) In all periods presented, there were no tax impacts related to rate changes and no amounts were reclassified to earnings. (4) Realized gains and losses were included in Other income, net on the accompanying Statement of Consolidated Operations. (5) These amounts were included in Sales on the accompanying Statement of Consolidated Operations. (6) These amounts were included in Cost of goods sold on the accompanying Statement of Consolidated Operations. (7) These amounts were included in Interest expense on the accompanying Statement of Consolidated Operations. (8) A positive amount indicates a corresponding charge to earnings and a negative amount indicates a corresponding benefit to earnings. These amounts were reflected on the accompanying Statement of Consolidated Operations in the line items indicated in footnotes 1 through 7.

Separation Transaction and Di35

Separation Transaction and Discontinued Operations (Tables)	12 Months Ended
	Dec. 31, 2017
Discontinued Operations and Disposal Groups [Abstract]
Summary of Discontinued Operations in Financial Statements	The results of operations of Alcoa Corporation were presented as discontinued operations in the Statement of Consolidated Operations as summarized below: Ten months ended October 31, Year ended December 31, 2016 2015 Sales $ 6,752 $ 10,121 Cost of goods sold (exclusive of expenses below) 5,655 7,965 Selling, general administrative, and other expenses 164 214 Research and development 28 69 Provision for depreciation, depletion and amortization 593 772 Restructuring and other charges 102 981 Interest expense 28 25 Other (income) expenses, net (75 ) 30 Income from discontinued operations before income taxes 257 65 Provision for income taxes 73 106 Income (loss) from discontinued operations after income taxes 184 (41 ) Less: Net income from discontinued operations attributable to noncontrolling interests 63 124 Net income (loss) from discontinued operations $ 121 $ (165 )
Disposal Groups, Including Discontinued Operations, Schedule Of Depreciation, Depletion, And Amortization	The following table presents depreciation, depletion and amortization, restructuring and other charges, and purchases of property, plant and equipment of the discontinued operations related to Alcoa Corporation: For the year ended December 31, 2016 2015 Depreciation, depletion and amortization $ 593 $ 772 Restructuring and other charges $ 102 $ 981 Capital expenditures $ 298 $ 391

Restructuring and Other Charg36

Restructuring and Other Charges (Tables)	12 Months Ended
	Dec. 31, 2017
Restructuring and Related Activities [Abstract]
Schedule of Restructuring and Other Charges	Restructuring and other charges for each year in the three-year period ended December 31, 2017 were comprised of the following: 2017 2016 2015 Asset impairments $ 58 $ 80 $ — Layoff costs 64 70 97 Net loss on divestitures of businesses (F) 57 3 136 Other (3 ) 27 (11 ) Reversals of previously recorded layoff costs (11 ) (25 ) (8 ) Restructuring and other charges $ 165 $ 155 $ 214
Schedule of Restructuring and Other Charges by Reportable Segments, Pretax	The pre-tax impact of allocating such charges to segment results would have been as follows: 2017 2016 2015 Engineered Products and Solutions $ 30 $ 78 $ 46 Global Rolled Products 72 40 121 Transportation and Construction Solutions 52 14 8 Segment total 154 132 175 Corporate 11 23 39 Total restructuring and other charges $ 165 $ 155 $ 214
Activity and Reserve Balances for Restructuring Charges	Activity and reserve balances for restructuring charges were as follows: Layoff costs Other exit costs Total Reserve balances at December 31, 2014 $ 48 $ 20 $ 68 2015: Cash payments (45 ) (12 ) (57 ) Restructuring charges 97 7 104 Other* (16 ) (6 ) (22 ) Reserve balances at December 31, 2015 84 9 93 2016: Cash payments (73 ) (13 ) (86 ) Restructuring charges 70 27 97 Other* (31 ) (14 ) (45 ) Reserve balances at December 31, 2016 50 9 59 2017: Cash payments (59 ) (6 ) (65 ) Restructuring charges 64 1 65 Other* 1 (2 ) (1 ) Reserve balances at December 31, 2017 $ 56 $ 2 $ 58 * Other includes reversals of previously recorded restructuring charges and the effects of foreign currency translation. In 2017, Other for layoff costs also includes the reclassification of a stock awards reversal of $13 . In 2016, Other for other exit costs also included a reclassification of $8 in asset retirement and $2 in environmental obligations, as these liabilities were included in Arconic’s separate reserves for asset retirement obligations and environmental remediation. Other for other exit costs also included a reclassification of $4 in legal obligations, as these liabilities were included in Arconic’s separate reserves for legal costs. In 2015, Other for other exit costs included a reclassification of $5 for certain obligations included in Arconic’s separate reserves for warranties, lease terminations and tax indemnities.

Goodwill and Other Intangible37

Goodwill and Other Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Changes in Carrying Amount of Goodwill	The following table details the changes in the carrying amount of goodwill: Engineered Global Rolled Products Transportation and Construction Solutions Corporate* Total Balances at December 31, 2015 Goodwill $ 4,660 $ 201 $ 111 $ 330 $ 5,302 Accumulated impairment losses — — (53 ) — (53 ) 4,660 201 58 330 5,249 Acquisitions and Divestitures (F) 47 — — — 47 Translation and other (128 ) (20 ) (1 ) 1 (148 ) Balances at December 31, 2016 Goodwill 4,579 181 110 331 5,201 Accumulated impairment losses — — (53 ) — (53 ) 4,579 181 57 331 5,148 Impairment (A) (719 ) — — — (719 ) Translation and other 89 12 3 2 106 Balances at December 31, 2017 Goodwill 4,668 193 113 333 5,307 Accumulated impairment losses (719 ) — (53 ) — (772 ) $ 3,949 $ 193 $ 60 $ 333 $ 4,535 * As of December 31, 2017 , the amount reflected in Corporate is allocated to Arconic’s three reportable segments ( $256 to Engineered Products and Solutions, $59 to Global Rolled Products and $18 to Transportation and Construction Solutions) for purposes of impairment testing (see Goodwill policy in Note A). This goodwill is reflected in Corporate for segment reporting purposes because it is not included in management’s assessment of performance by the three reportable segments.
Other Intangible Assets	Other intangible assets were as follows: December 31, 2017 Gross carrying amount Accumulated amortization Computer software $ 789 $ (674 ) Patents and licenses 110 (107 ) Other intangibles 953 (116 ) Total amortizable intangible assets 1,852 (897 ) Indefinite-lived trade names and trademarks 32 — Total other intangible assets $ 1,884 $ (897 ) December 31, 2016 Gross carrying amount Accumulated amortization Computer software $ 755 $ (623 ) Patents and licenses 110 (102 ) Other intangibles 897 (81 ) Total amortizable intangible assets 1,762 (806 ) Indefinite-lived trade names and trademarks 32 — Total other intangible assets $ 1,794 $ (806 )

Inventories (Tables)

Inventories (Tables)	12 Months Ended
	Dec. 31, 2017
Inventory Disclosure [Abstract]
Schedule of Inventory Components	December 31, 2017 2016 Finished goods $ 669 $ 625 Work-in-process 1,349 1,144 Purchased raw materials 381 408 Operating supplies 81 76 $ 2,480 $ 2,253

Properties, Plants, and Equip39

Properties, Plants, and Equipment, Net (Tables)	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Schedule of Properties, Plants, and Equipment, Net	December 31, 2017 2016 Land and land rights $ 140 $ 135 Structures: Engineered Products and Solutions 784 733 Global Rolled Products 1,090 1,061 Transportation and Construction Solutions 268 254 Other 253 248 2,395 2,296 Machinery and equipment: Engineered Products and Solutions 3,054 2,728 Global Rolled Products 4,641 4,570 Transportation and Construction Solutions 777 723 Other 358 337 8,830 8,358 11,365 10,789 Less: accumulated depreciation and amortization 6,392 6,073 4,973 4,716 Construction work-in-progress 621 783 $ 5,594 $ 5,499

Debt (Tables)

Debt (Tables)	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Schedule of Long-Term Debt	Long-Term Debt. December 31, 2017 2016 6.50% Bonds, due 2018 $ — $ 250 6.75% Notes, due 2018 — 750 5.72% Notes, due 2019 500 750 1.63% Convertible Notes, due 2019* 403 403 6.150% Notes, due 2020 1,000 1,000 5.40% Notes, due 2021 1,250 1,250 5.87% Notes, due 2022 627 627 5.125% Notes, due 2024 1,250 1,250 5.90% Notes, due 2027 625 625 6.75% Bonds, due 2028 300 300 5.95% Notes due 2037 625 625 Iowa Finance Authority Loan, due 2042 (4.75%) 250 250 Other** (23 ) (32 ) 6,807 8,048 Less: amount due within one year 1 4 $ 6,806 $ 8,044 * Amount was assumed in conjunction with the acquisition of RTI (see Note F). ** Other includes various financing arrangements related to subsidiaries, unamortized debt discounts related to the outstanding notes and bonds listed in the table above, an equity option related to the convertible notes due in 2019 (see Note F), adjustments to the carrying value of long-term debt related to an interest swap contract accounted for as a fair value hedge that was unwound during 2017, and unamortized debt issuance costs.

Other Noncurrent Liabilities 41

Other Noncurrent Liabilities and Deferred Credits (Tables)	12 Months Ended
	Dec. 31, 2017
Payables and Accruals [Abstract]
Schedule of Other Noncurrent Liabilities and Deferred Credits	December 31, 2017 2016 Environmental remediation (L) $ 253 $ 260 Income taxes (Q) 162 154 Accrued compensation and retirement costs 218 216 Contingent payment related to an acquisition (F) — 78 Other 126 162 $ 759 $ 870

Other Income, Net (Tables)

Other Income, Net (Tables)	12 Months Ended
	Dec. 31, 2017
Other Income and Expenses [Abstract]
Schedule of Other Expenses (Income), Net	2017 2016 2015 Equity income $ — $ (7 ) $ — Interest income (19 ) (16 ) (16 ) Foreign currency (gains) losses, net (5 ) (4 ) 51 Net (gain) loss from asset sales (513 ) 11 (42 ) Net loss (gain) on mark-to-market derivative contracts — 1 (3 ) Other, net (103 ) (79 ) (18 ) $ (640 ) $ (94 ) $ (28 )

Cash Flow Information (Tables)

Cash Flow Information (Tables)	12 Months Ended
	Dec. 31, 2017
Supplemental Cash Flow Information [Abstract]
Schedule of Cash Paid for Interest and Income Taxes	Cash paid for interest and income taxes was as follows: 2017 2016 2015 Interest, net of amount capitalized $ 508 $ 524 $ 487 Income taxes, net of amount refunded $ 118 $ 324 $ 345
Schedule of Cash Paid for Acquisitions Including Non-Controlling Interest	The details related to cash paid for acquisitions were as follows: 2017 2016 2015 Assets acquired $ — $ — $ 2,003 Liabilities assumed — — (868 ) Equity issued — — (870 ) Working capital adjustment — (10 ) — Increase in Arconic’s shareholders’ equity — — (60 ) Cash paid — (10 ) 205 Less: cash acquired — — 302 Net cash paid $ — $ (10 ) $ (97 )

Segment and Geographic Area I44

Segment and Geographic Area Information (Tables)	12 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
Schedule of Operating Results and Assets of Arconic's Reportable Segments	The operating results and assets of Arconic’s reportable segments were as follows: Engineered Products and Solutions Global Rolled Products Transportation and Construction Solutions Total 2017 Sales: Third-party sales $ 5,935 $ 4,992 $ 1,985 $ 12,912 Intersegment sales — 148 — 148 Total sales $ 5,935 $ 5,140 $ 1,985 $ 13,060 Profit and loss: Depreciation and amortization 268 205 50 523 Adjusted EBITDA 1,224 599 321 2,144 2016 Sales: Third-party sales $ 5,728 $ 4,864 $ 1,802 $ 12,394 Intersegment sales — 118 — 118 Total sales $ 5,728 $ 4,982 $ 1,802 $ 12,512 Profit and loss: Depreciation and amortization $ 255 $ 201 $ 48 $ 504 Adjusted EBITDA 1,195 577 291 2,063 2015 Sales: Third-party sales $ 5,342 $ 5,253 $ 1,882 $ 12,477 Intersegment sales — 125 — 125 Total sales $ 5,342 $ 5,378 $ 1,882 $ 12,602 Profit and loss: Depreciation and amortization $ 233 $ 203 $ 43 $ 479 Adjusted EBITDA 1,111 512 271 1,894 2017 Assets: Capital expenditures $ 308 $ 178 $ 57 $ 543 Goodwill 3,949 193 60 4,202 Total assets 10,252 4,179 1,068 15,499 2016 Assets: Capital expenditures $ 333 $ 293 $ 63 $ 689 Goodwill 4,579 181 57 4,817 Total assets 10,542 3,891 982 15,415
Schedule of Reconciliation of Certain Segment Information to Consolidated Totals	The following tables reconcile certain segment information to consolidated totals: 2017 2016 2015 Sales: Total segment sales $ 13,060 $ 12,512 $ 12,602 Elimination of intersegment sales (148 ) (118 ) (125 ) Corporate 48 — (64 ) Consolidated sales $ 12,960 $ 12,394 $ 12,413
Schedule of Segment ATOI to Consolidated Net (Loss) Income Attributable to Arconic	2017 2016 2015 Combined segment adjusted EBITDA $ 2,144 $ 2,063 $ 1,894 Unallocated amounts: Depreciation and amortization (551 ) (535 ) (508 ) Impairment of goodwill (719 ) — (25 ) Restructuring and other charges (165 ) (155 ) (214 ) Impact of LIFO (110 ) (18 ) 101 Metal price lag 72 27 (175 ) Corporate expense (274 ) (454 ) (371 ) Other (71 ) (109 ) (74 ) Operating income 326 819 628 Interest expense (496 ) (499 ) (473 ) Other income, net 640 94 28 Income from continuing operations before income taxes 470 414 183 Provision for income taxes (544 ) (1,476 ) (339 ) Discontinued operations — 121 (165 ) Net income attributable to noncontrolling interest — — (1 ) Net loss attributable to Arconic $ (74 ) $ (941 ) $ (322 )
Schedule of Segment Reporting Information to Consolidated Assets	December 31, 2017 2016 Assets: Total segment assets $ 15,499 $ 15,415 Unallocated amounts: Cash and cash equivalents 2,150 1,863 Deferred income taxes 743 1,234 Corporate goodwill 333 331 Corporate fixed assets, net 310 308 LIFO reserve (481 ) (371 ) Fair value of derivative contracts 91 24 Investment in common stock of Alcoa Corporation — 1,020 Other 73 214 Consolidated assets $ 18,718 $ 20,038
Sales by Major Product Grouping	Sales by major product grouping were as follows: 2017 2016 2015 Sales: Flat-rolled aluminum $ 4,992 $ 4,864 $ 5,253 Fastening systems and rings 2,102 2,060 2,168 Investment castings 1,983 1,870 1,812 Other extruded and forged products 1,565 1,495 1,332 Architectural aluminum systems 1,065 1,010 951 Aluminum wheels 805 689 790 Other 448 406 107 $ 12,960 $ 12,394 $ 12,413
Schedule of Geographic Information for Sales	Geographic information for sales was as follows (based upon the country where the point of sale occurred): 2017 2016 2015 Sales: United States $ 8,167 $ 7,823 $ 8,044 France 965 930 802 Hungary 739 619 622 United Kingdom 721 711 698 China 615 582 565 Russia 500 433 455 Germany 309 284 264 Brazil 285 250 297 Canada 261 262 180 Japan 141 145 138 Italy 37 127 139 Other 220 228 209 $ 12,960 $ 12,394 $ 12,413
Schedule of Geographic Information for Long-Lived Assets	Geographic information for long-lived assets was as follows (based upon the physical location of the assets): December 31, 2017 2016 Long-lived assets: United States $ 4,005 $ 3,966 China 347 336 Russia 276 295 United Kingdom 259 232 Hungary 227 194 France 159 118 Germany 88 64 Canada 63 58 Brazil 62 97 Other 108 139 $ 5,594 $ 5,499

Preferred and Common Stock (Tab

Preferred and Common Stock (Tables)	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Schedule of Share Activity	Share Activity (number of shares) Common stock Treasury Outstanding Balance at end of 2014 87,150,169 1,216,663,661 Issued for stock-based compensation plans (6,099,066 ) 6,099,066 Acquisition of RTI — 87,397,414 Balance at end of 2015 81,051,103 1,310,160,141 Issued for stock-based compensation plans (5,219,660 ) 5,302,128 Treasury stock retirement (75,831,443 ) — Reverse Stock Split — (876,942,489 ) Balance at end of 2016 — 438,519,780 Conversion of convertible notes — 39,242,706 Issued for stock-based compensation plans — 3,654,051 Balance at end of 2017 — 481,416,537
Schedule of Activity for Stock Options and Stock Awards	The activity for stock options and stock awards during 2017 was as follows (options and awards in millions): Stock options Stock awards Number of options Weighted average exercise price Number of awards Weighted average FMV per award Outstanding, January 1, 2017 13 $ 24.14 8 $ 22.26 Granted 2 21.13 3 21.86 Exercised (2 ) 20.65 — — Converted — — (2 ) 24.95 Expired or forfeited (2 ) 25.99 (2 ) 21.26 Performance share adjustment — — — 21.48 Outstanding, December 31, 2017 11 23.94 7 21.49

Earnings Per Share (Tables)

Earnings Per Share (Tables)	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Reconciliation of Information Used to Compute Basic and Diluted EPS	The information used to compute basic and diluted EPS attributable to Arconic common shareholders was as follows (shares in millions): 2017 2016 2015 Net loss from continuing operations attributable to Arconic $ (74 ) $ (1,062 ) $ (156 ) Net income from continuing operations attributable to noncontrolling interests — — (1 ) Less: preferred stock dividends declared (53 ) (69 ) (69 ) Loss from continuing operations available to Arconic common shareholders (127 ) (1,131 ) (226 ) Income (loss) from discontinued operations after income taxes and noncontrolling interests (1) — 121 (165 ) Net loss available to Arconic common shareholders—basic (127 ) (1,010 ) (391 ) Add: interest expense related to convertible notes — — — Add: dividends related to mandatory convertible preferred stock — — — Net loss available to Arconic common shareholders—diluted $ (127 ) $ (1,010 ) $ (391 ) Average shares outstanding—basic 451 438 420 Effect of dilutive securities: Stock options — — — Stock and performance awards — — — Mandatory convertible preferred stock — — — Convertible notes — — — Average shares outstanding—diluted 451 438 420 (1) Calculated from the Statement of Consolidated Operations as Income (loss) from discontinued operations after income taxes less Net income from discontinued operations attributable to noncontrolling interests.

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Components of Income from Continuing Operations Before Income Taxes	The components of income from continuing operations before income taxes were as follows: 2017 2016 2015 United States $ 500 $ 84 $ 124 Foreign (30 ) 330 59 $ 470 $ 414 $ 183
Schedule of Provision for Income Taxes on Income from Continuing Operations	The provision for income taxes consisted of the following: 2017 2016 2015 Current: Federal* $ — $ — $ — Foreign 98 133 115 State and local (2 ) 1 (1 ) 96 134 114 Deferred: Federal* 489 1,208 196 Foreign 37 136 29 State and local (78 ) (2 ) — 448 1,342 225 Total $ 544 $ 1,476 $ 339 * Includes U.S. taxes related to foreign income
Reconciliation of U.S. Federal Statutory Rate to Arconic's Effective Tax Rate	A reconciliation of the U.S. federal statutory rate to Arconic’s effective tax rate was as follows (the effective tax rate for all periods was a provision on income): 2017 2016 2015 U.S. federal statutory rate 35.0 % 35.0 % 35.0 % Taxes on foreign operations (7.5 ) (10.2 ) 2.5 Federal benefit of state tax 3.1 0.4 0.3 Permanent differences on restructuring and other charges and asset disposals (1) (167.4 ) (107.8 ) 3.6 Non-deductible acquisition costs 0.3 8.4 7.1 Statutory tax rate and law changes (2) 52.5 (15.7 ) (1.0 ) Tax holidays (3.0 ) (0.8 ) (3.9 ) Tax credits (0.7 ) (1.2 ) (2.8 ) Changes in valuation allowances 137.9 426.8 145.8 Impairment of goodwill 53.5 — 4.8 Company-owned life insurance/split-dollar net premiums — 23.0 (3.0 ) Changes in uncertain tax positions 10.1 2.1 (2.2 ) Other 1.9 (3.5 ) (1.0 ) Effective tax rate 115.7 % 356.5 % 185.2 % (1) Additional losses were reported in Spain's 2017 tax return related to the Separation Transaction which are offset by an increased valuation allowance. (2) On December 22, 2017, the United States enacted the Tax Cuts and Jobs Act of 2017 ("the 2017 Act”) resulting in significant changes to the Internal Revenue Code (see below). In December 2016, Spain and the United States enacted tax law changes which resulted in the remeasurement of certain deferred tax liabilities recorded by Arconic.
Schedule of Components of Net Deferred Tax Assets and Liabilities	The components of net deferred tax assets and liabilities were as follows: 2017 2016 December 31, Deferred tax assets Deferred tax liabilities Deferred tax assets Deferred tax liabilities Depreciation $ 31 $ 693 $ 15 $ 817 Employee benefits 936 23 1,382 8 Loss provisions 134 14 181 1 Deferred income/expense 19 1,144 20 74 Tax loss carryforwards 3,305 — 1,540 — Tax credit carryforwards 638 — 652 — Other 24 33 164 19 5,087 1,907 3,954 919 Valuation allowance (2,584 ) — (1,940 ) — $ 2,503 $ 1,907 $ 2,014 $ 919
Schedule of Expiration Periods of Deferred Tax Assets	The following table details the expiration periods of the deferred tax assets presented above: December 31, 2017 Expires within 10 years Expires within 11-20 years No expiration* Other* Total Tax loss carryforwards $ 81 $ 781 $ 2,443 $ — $ 3,305 Tax credit carryforwards 531 97 10 — 638 Other — — 84 1,060 1,144 Valuation allowance (467 ) (646 ) (1,376 ) (95 ) (2,584 ) $ 145 $ 232 $ 1,161 $ 965 $ 2,503 * Deferred tax assets with no expiration may still have annual limitations on utilization. Other represents deferred tax assets whose expiration is dependent upon the reversal of the underlying temporary difference. A substantial amount of Other relates to employee benefits that will become deductible for tax purposes over an extended period of time as contributions are made to employee benefit plans and payments are made to retirees.
Schedule of Changes in Valuation Allowance	The following table details the changes in the valuation allowance: December 31, 2017 2016 2015 Balance at beginning of year $ 1,940 $ 1,291 $ 1,151 Increase to allowance 831 772 180 Release of allowance (246 ) (209 ) (42 ) Acquisitions and divestitures (F) (1 ) (1 ) 29 Tax apportionment, tax rate and tax law changes (24 ) 106 (15 ) Foreign currency translation 84 (19 ) (12 ) Balance at end of year $ 2,584 $ 1,940 $ 1,291
Reconciliation of Unrecognized Tax Benefits (Excluding Interest and Penalties)	A reconciliation of the beginning and ending amount of unrecognized tax benefits (excluding interest and penalties) was as follows: December 31, 2017 2016 2015 Balance at beginning of year $ 28 $ 18 $ 7 Additions for tax positions of the current year 23 12 — Additions for tax positions of prior years 27 — 14 Reductions for tax positions of prior years — — (2 ) Settlements with tax authorities — (1 ) — Expiration of the statute of limitations (5 ) (1 ) (1 ) Foreign currency translation — — — Balance at end of year $ 73 $ 28 $ 18

Receivables (Tables)

Receivables (Tables)	12 Months Ended
	Dec. 31, 2017
Transfers and Servicing [Abstract]
Schedule of Allowance for Doubtful Accounts	The following table details the changes in the allowance for doubtful accounts related to customer receivables and other receivables: Customer receivables Other receivables December 31, 2017 2016 2015 2017 2016 2015 Balance at beginning of year $ 13 $ 8 $ 6 $ 32 $ 34 $ 24 Provision for doubtful accounts 1 7 4 9 6 8 Write off of uncollectible accounts (5 ) (3 ) (2 ) (1 ) (1 ) 2 Recoveries of prior write-offs — (1 ) — (3 ) 1 (1 ) Other (1 ) 2 — (3 ) (8 ) 1 Balance at end of year $ 8 $ 13 $ 8 $ 34 $ 32 $ 34

Interest Cost Components (Table

Interest Cost Components (Tables)	12 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Schedule of Interest Cost Components	2017 2016 2015 Amount charged to expense $ 496 $ 499 $ 473 Amount capitalized 22 32 27 $ 518 $ 531 $ 500

Pension and Other Postretirem50

Pension and Other Postretirement Benefits (Tables)	12 Months Ended
	Dec. 31, 2017
Retirement Benefits [Abstract]
Schedule of Obligations and Funded Status	Obligations and Funded Status Pension benefits Other postretirement benefits December 31, 2017 2016 2017 2016 Change in benefit obligation Benefit obligation at beginning of year $ 7,026 $ 14,247 $ 980 $ 2,319 Service cost 90 165 7 13 Interest cost 234 435 30 63 Amendments 1 2 — — Actuarial (gains) losses 311 770 1 112 Transfer to Alcoa Corporation — (7,577 ) — (1,340 ) Settlements — (82 ) — — Benefits paid, net of participants’ contributions (425 ) (794 ) (98 ) (197 ) Medicare Part D subsidy receipts — — 7 9 Foreign currency translation impact 122 (140 ) — 1 Benefit obligation at end of year (1) $ 7,359 $ 7,026 $ 927 $ 980 Change in plan assets (1) Fair value of plan assets at beginning of year $ 4,666 $ 10,928 $ — $ — Actual return on plan assets 212 89 — — Employer contributions 310 296 — — Participants’ contributions — 16 — — Benefits paid (404 ) (762 ) — — Administrative expenses (33 ) (65 ) — — Transfer to Alcoa Corporation — (5,610 ) — — Settlements — (82 ) — — Foreign currency translation impact 111 (144 ) — — Fair value of plan assets at end of year (1) $ 4,862 $ 4,666 $ — $ — Funded status* $ (2,497 ) $ (2,360 ) $ (927 ) $ (980 ) Less: Amounts attributed to joint venture partners — — — — Net funded status $ (2,497 ) $ (2,360 ) $ (927 ) $ (980 ) Amounts recognized in the Consolidated Balance Sheet consist of: Noncurrent assets $ 89 $ 6 $ — $ — Current liabilities (22 ) (21 ) (86 ) (91 ) Noncurrent liabilities (2,564 ) (2,345 ) (841 ) (889 ) Net amount recognized $ (2,497 ) $ (2,360 ) $ (927 ) $ (980 ) Amounts recognized in Accumulated Other Comprehensive Loss consist of: Net actuarial loss $ 3,240 $ 2,979 $ 146 $ 150 Prior service cost (benefit) 10 15 (37 ) (45 ) Total, before tax effect 3,250 2,994 109 105 Less: Amounts attributed to joint venture partners — — — — Net amount recognized, before tax effect $ 3,250 $ 2,994 $ 109 $ 105 Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Loss consist of: Net actuarial loss (gain) $ 481 $ (1,992 ) $ 1 $ (224 ) Amortization of accumulated net actuarial loss (220 ) (380 ) (5 ) (24 ) Prior service (benefit) cost — (42 ) — 37 Amortization of prior service (cost) benefit (5 ) (13 ) 8 24 Total, before tax effect 256 (2,427 ) 4 (187 ) Less: Amounts attributed to joint venture partners — 38 — — Net amount recognized, before tax effect $ 256 $ (2,389 ) $ 4 $ (187 ) (1) At December 31, 2017 , the benefit obligation, fair value of plan assets, and funded status for U.S. pension plans were $6,018 , $3,544 , and $(2,474) , respectively. At December 31, 2016 , the benefit obligation, fair value of plan assets, and funded status for U.S. pension plans were $5,707 , $3,495 , and $(2,212) , respectively.
Schedule of Pension Plan Benefit Obligations	Pension Plan Benefit Obligations Pension benefits 2017 2016 The projected benefit obligation and accumulated benefit obligation for all defined benefit pension plans was as follows: Projected benefit obligation $ 7,359 $ 7,026 Accumulated benefit obligation 7,169 6,850 The aggregate projected benefit obligation and fair value of plan assets for pension plans with projected benefit obligations in excess of plan assets was as follows: Projected benefit obligation 6,600 6,995 Fair value of plan assets 4,016 4,629 The aggregate accumulated benefit obligation and fair value of plan assets for pension plans with accumulated benefit obligations in excess of plan assets was as follows: Accumulated benefit obligation 6,422 6,104 Fair value of plan assets 3,998 3,894
Components of Net Periodic Benefit Cost	Components of Net Periodic Benefit Cost Pension benefits (1) Other postretirement benefits (2) 2017 2016 2015 2017 2016 2015 Service cost $ 90 $ 155 $ 175 $ 7 $ 13 $ 14 Interest cost 234 431 577 30 63 92 Expected return on plan assets (332 ) (677 ) (753 ) — — — Recognized net actuarial loss 220 380 468 5 24 17 Amortization of prior service cost (benefit) 5 13 16 (8 ) (24 ) (37 ) Settlements (3) — 19 16 — — — Curtailments (4) — — 9 — — (4 ) Special termination benefits (5) — 2 16 — — — Net periodic benefit cost (6) $ 217 $ 323 $ 524 $ 34 $ 76 $ 82 Discontinued operations — 122 248 — 41 43 Net amount recognized in Statement of Consolidated Operations $ 217 $ 201 $ 276 $ 34 $ 35 $ 39 Note: the footnotes below include components of Net Periodic Benefit Cost related to Alcoa Corporation through the completion of the Separation Transaction. (1) In 2017 , 2016 and 2015 , net periodic benefit cost for U.S. pension plans was $206 , $261 , and $423 , respectively. (2) In 2017 , 2016 and 2015 , net periodic benefit cost for other postretirement benefits reflects a reduction of $11 , $22 , and $34 , respectively, related to the recognition of the federal subsidy awarded under Medicare Part D. (3) In 2016, settlements were due to workforce reductions (see Note D) and the payment of lump sum benefits and/or purchases of annuity contracts. In 2015, settlements were due to workforce reductions (see Note D) and the payment of lump sum benefits and/or purchases of annuity contracts. (4) In 2015, curtailments were due to elimination of benefits or workforce reductions (see Note D). (5) In 2016 and 2015, special termination benefits were due to workforce reductions (see Note D). (6) Amounts attributed to joint venture partners are not included.
Schedule of Amounts Expected to be Recognized in Net Periodic Benefit Cost	Amounts Expected to be Recognized in Net Periodic Benefit Cost Pension benefits Other postretirement benefits 2018 2018 Net actuarial loss recognition 168 9 Prior service cost (benefit) recognition 3 (8 )
Schedule of Weighted Average Assumptions Used to Determine Benefit Obligations and Net Periodic Benefit Cost	Weighted average assumptions used to determine net periodic benefit cost for U.S. pension and other postretirement benefit plans were as follows (assumptions for non-U.S. plans did not differ materially): 2017 2016 2015 Discount rate to calculate service cost* 4.20 % 4.29 % 4.00 % Discount rate to calculate interest cost* 3.60 3.15 4.00 Expected long-term rate of return on plan assets 7.75 7.75 7.75 Rate of compensation increase 3.50 3.50 3.50 * In all periods presented, the respective discount rates were used to determine net periodic benefit cost for most U.S. pension plans for the full annual period. However, the discount rates for a limited number of plans were updated during 2017 , 2016 , and 2015 to reflect the remeasurement of these plans due to new union labor agreements, settlements, and/or curtailments. The updated discount rates used were not significantly different from the discount rates presented. Weighted average assumptions used to determine benefit obligations for U.S. pension and other postretirement benefit plans were as follows (assumptions for non-U.S. plans did not differ materially): December 31, 2017 2016 Discount rate 3.75 % 4.20 % Rate of compensation increase 3.50 3.50
Schedule of Assumed Health Care Cost Trend Rates	Assumed health care cost trend rates for U.S. other postretirement benefit plans were as follows (assumptions for non-U.S. plans did not differ materially): 2017 2016 2015 Health care cost trend rate assumed for next year 5.50 % 5.50 % 5.50 % Rate to which the cost trend rate gradually declines 4.50 % 4.50 % 4.50 % Year that the rate reaches the rate at which it is assumed to remain 2021 2020 2019
Schedule of One-Percentage Point Change in Assumed Rates of Health Care Cost Trend Rates	Assumed health care cost trend rates have an effect on the amounts reported for the health care plan. A one-percentage point change in these assumed rates would have the following effects: 1% increase 1% decrease Effect on other postretirement benefit obligations $ 29 $ (28 ) Effect on total of service and interest cost components 1 (1 )
Schedule of Pension and Postretirement Plans Investment Policy and Weighted Average Asset Allocations	Arconic’s pension plans’ investment policy and weighted average asset allocations at December 31, 2017 and 2016 , by asset class, were as follows: Plan assets at December 31, Asset class Policy range 2017 2016 Equities 20–55% 28 % 30 % Fixed income 25–55% 47 42 Other investments 15–35% 25 28 Total 100 % 100 % The following table presents the fair value of pension plan assets classified under the appropriate level of the fair value hierarchy or net asset cost: December 31, 2017 Level 1 Level 2 Net asset value Total Equities: Equity securities $ 379 $ — $ 593 $ 972 Long/short equity hedge funds — — 230 230 Private equity — — 155 155 $ 379 $ — $ 978 $ 1,357 Fixed income: Intermediate and long duration government/credit $ 201 $ 981 $ 779 $ 1,961 Other 164 8 145 317 $ 365 $ 989 $ 924 $ 2,278 Other investments: Real estate $ 85 $ — $ 172 $ 257 Discretionary and systematic macro hedge funds — — 583 583 Other 77 7 275 359 $ 162 $ 7 $ 1,030 $ 1,199 Net plan assets* $ 906 $ 996 $ 2,932 $ 4,834 December 31, 2016 Level 1 Level 2 Net Asset Value Total Equities Equity securities $ 393 $ — $ 431 $ 824 Long/short equity hedge funds — — 406 406 Private equity — — 165 165 $ 393 $ — $ 1,002 $ 1,395 Fixed income: Intermediate and long duration government/credit $ 23 $ 95 $ 655 $ 773 Other 1,060 51 74 1,185 $ 1,083 $ 146 $ 729 $ 1,958 Other investments: Real estate $ 81 $ — $ 185 $ 266 Discretionary and systematic macro hedge funds — — 784 784 Other 65 — 178 243 $ 146 $ — $ 1,147 $ 1,293 Net plan assets** $ 1,622 $ 146 $ 2,878 $ 4,646 * As of December 31, 2017 , the total fair value of pension plans’ assets excludes a net receivable of $28 , which represents assets due from Alcoa Corporation as a result of plan separations and securities sold but not yet settled plus interest and dividends earned on various investments. ** As of December 31, 2016 , the total fair value of pension plans’ assets excludes a net receivable of $20 , which represents assets due from Alcoa Corporation as a result of plan separations and securities sold not yet settled plus interest and dividends earned on various investments.
Schedule of Benefit Payments Expected to be Paid and Expected Medicare Part D Subsidy Receipts	Benefit payments expected to be paid to pension and other postretirement benefit plans’ participants and expected Medicare Part D subsidy receipts are as follows utilizing the current assumptions outlined above: Year ended December 31, Pension benefits paid Gross Other post- retirement benefits Medicare Part D subsidy receipts Net Other post- retirement benefits 2018 $ 435 $ 90 $ 5 $ 85 2019 440 90 5 85 2020 440 90 5 85 2021 445 90 5 85 2022 450 90 5 85 Thereafter 2,265 335 25 310 $ 4,475 $ 785 $ 50 $ 735

Other Financial Instruments (Ta

Other Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of Carrying Values and Fair Values of Other Financial Instruments	The carrying values and fair values of Arconic’s financial instruments were as follows: 2017 2016 December 31, Carrying value Fair value Carrying value Fair value Cash and cash equivalents $ 2,150 $ 2,150 $ 1,863 $ 1,863 Restricted cash 4 4 15 15 Derivatives – current asset 61 61 14 14 Noncurrent receivables 20 20 21 21 Derivatives – noncurrent asset 33 33 10 10 Available-for-sale securities 106 106 102 102 Investment in common stock of Alcoa Corporation — — 1,020 1,020 Short-term debt 38 38 40 40 Derivatives – current liability 45 45 5 5 Commercial paper — — — — Derivatives – noncurrent liability 14 14 3 3 Contingent payment related to an acquisition — — 78 78 Long-term debt, less amount due within one year 6,806 7,443 8,044 8,519

Quarterly Data (Tables)

Quarterly Data (Tables)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Schedule of Quarterly Data	Supplemental Financial Information (unaudited) Quarterly Data (in millions, except per-share amounts) First Second Third Fourth (2) Year 2017 Sales $ 3,192 $ 3,261 $ 3,236 $ 3,271 $ 12,960 Net income (loss) attributable to Arconic $ 322 $ 212 $ 119 $ (727 ) $ (74 ) Earnings (loss) per share attributable to Arconic common shareholders (1) : Basic Net income (loss) per share—basic $ 0.69 $ 0.44 $ 0.23 $ (1.51 ) $ (0.28 ) Diluted Net income (loss) per share—diluted $ 0.65 $ 0.43 $ 0.22 $ (1.51 ) $ (0.28 ) 2016 Sales $ 3,055 $ 3,234 $ 3,138 $ 2,967 $ 12,394 Net income (loss) attributable to Arconic $ 16 $ 135 $ 166 $ (1,258 ) $ (941 ) Earnings (loss) per share attributable to Arconic common shareholders (1) : Basic Continuing operations $ 0.21 $ 0.08 $ 0.11 $ (2.98 ) $ (2.58 ) Discontinued operations (0.21 ) 0.19 0.23 0.07 0.27 Net income (loss) per share—basic $ 0.00 $ 0.27 $ 0.34 $ (2.91 ) $ (2.31 ) Diluted Continuing operations $ 0.21 $ 0.08 $ 0.11 $ (2.98 ) $ (2.58 ) Discontinued operations (0.21 ) 0.19 0.22 0.07 0.27 Net income (loss) per share—basic $ 0.00 $ 0.27 $ 0.33 $ (2.91 ) $ (2.31 ) (1) Per share amounts are calculated independently for each period presented; therefore, the sum of the quarterly per share amounts may not equal the per share amounts for the year. (2) In the fourth quarter of 2017, Arconic recorded an impairment of goodwill related to the forgings and extrusions business of $719 ( $719 pre-tax); a provisional charge of $272 associated with the revaluation of U.S. net deferred tax assets due to a decrease in the U.S. corporate tax rate from 35% to 21% , as well as a one-time transition tax on the non-previously taxed earnings and profits of certain U.S.-owned foreign corporations as of December 31, 2017; a favorable adjustment to the Firth Rixson earn-out liability of $81 ( $81 pre-tax); and a favorable adjustment to a separation-related guarantee liability of $18 ( $25 pre-tax). In the fourth quarter of 2016, as a result of the Separation Transaction, Arconic recorded a charge of $1,267 for valuation allowances on certain deferred tax assets.

Summary of Significant Accoun53

Summary of Significant Accounting Policies - Additional Information (Detail)	3 Months Ended			12 Months Ended
	Mar. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2017USD ($)reporting_unit	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Summary Of Significant Accounting Policies [Line Items]
Original maturity of cash equivalents				3 months
Number of reporting units | reporting_unit				8
Segment allocation, goodwill recognized		$ 4,535,000,000	$ 5,249,000,000	$ 4,535,000,000	$ 5,148,000,000	$ 5,249,000,000
Minimum percentage of estimated fair value of reporting unit to be less than carrying amount of goodwill				50.00%
Period required for impairment testing of reporting units				3 years
Goodwill impairment				$ 719,000,000	0	25,000,000
Businesses expected to be disposed within, years				1 year
Adjustments for New Accounting Pronouncement | Pro Forma
Summary Of Significant Accounting Policies [Line Items]
New accounting pronouncement or change in accounting principle, effect of change on operating results				$ 154,000,000	$ 135,000,000
Adjustments for New Accounting Pronouncement | Scenario, Forecast
Summary Of Significant Accounting Policies [Line Items]
New accounting pronouncement or change in accounting principle, effect of change on operating results	$ 20,000,000
Engineered Products and Solutions
Summary Of Significant Accounting Policies [Line Items]
Number of reporting units | reporting_unit				4
Number of reporting units for goodwill allocation | reporting_unit				2
Number of reporting units being subjected to goodwill impairment test | reporting_unit				6
Goodwill impairment		719,000,000		$ 719,000,000
Engineered Products and Solutions | Fastening systems and rings
Summary Of Significant Accounting Policies [Line Items]
Segment allocation, goodwill recognized		2,221,000,000		2,221,000,000
Engineered Products and Solutions | Alcoa Power and Propulsion
Summary Of Significant Accounting Policies [Line Items]
Segment allocation, goodwill recognized		1,686,000,000		$ 1,686,000,000
Engineered Products and Solutions | Alcoa Forging and Extrusions
Summary Of Significant Accounting Policies [Line Items]
Goodwill impairment		$ 719,000,000
Transportation and Construction Solutions
Summary Of Significant Accounting Policies [Line Items]
Number of reporting units | reporting_unit				3
Goodwill impairment						25,000,000
Other Operating Segments
Summary Of Significant Accounting Policies [Line Items]
Qualitative assessment for reporting units | reporting_unit				1
Primary Metals
Summary Of Significant Accounting Policies [Line Items]
Goodwill impairment			$ 25,000,000
Implied fair value of goodwill						$ 0
Minimum | Engineered Products and Solutions
Summary Of Significant Accounting Policies [Line Items]
Percentage of total goodwill allocated to two reporting units				85.00%

Summary of Significant Accoun54

Summary of Significant Accounting Policies - Weighted-Average Useful Lives of Structures and Machinery and Equipment (Detail)	12 Months Ended
	Dec. 31, 2017
Structures | Engineered Products and Solutions
Property, Plant and Equipment [Line Items]
Weighted-average useful lives of assets, years	29 years
Structures | Global Rolled Products
Property, Plant and Equipment [Line Items]
Weighted-average useful lives of assets, years	31 years
Structures | Transportation and Construction Solutions
Property, Plant and Equipment [Line Items]
Weighted-average useful lives of assets, years	27 years
Machinery and equipment | Engineered Products and Solutions
Property, Plant and Equipment [Line Items]
Weighted-average useful lives of assets, years	17 years
Machinery and equipment | Global Rolled Products
Property, Plant and Equipment [Line Items]
Weighted-average useful lives of assets, years	21 years
Machinery and equipment | Transportation and Construction Solutions
Property, Plant and Equipment [Line Items]
Weighted-average useful lives of assets, years	18 years

Summary of Significant Accoun55

Summary of Significant Accounting Policies - Weighted-Average Useful Lives of Software and Other Intangible Assets (Detail)	12 Months Ended
	Dec. 31, 2017
Software | Engineered Products and Solutions
Finite-Lived Intangible Assets [Line Items]
Weighted-average useful lives of other intangible assets	6 years
Software | Global Rolled Products
Finite-Lived Intangible Assets [Line Items]
Weighted-average useful lives of other intangible assets	6 years
Software | Transportation and Construction Solutions
Finite-Lived Intangible Assets [Line Items]
Weighted-average useful lives of other intangible assets	5 years
Other intangible assets | Engineered Products and Solutions
Finite-Lived Intangible Assets [Line Items]
Weighted-average useful lives of other intangible assets	34 years
Other intangible assets | Global Rolled Products
Finite-Lived Intangible Assets [Line Items]
Weighted-average useful lives of other intangible assets	9 years
Other intangible assets | Transportation and Construction Solutions
Finite-Lived Intangible Assets [Line Items]
Weighted-average useful lives of other intangible assets	16 years

Accumulated Other Comprehensi56

Accumulated Other Comprehensive Loss - Summary of Changes in Accumulated Other Comprehensive (Loss) Income by Component (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pension and other postretirement benefits
Balance at beginning of period	$ (2,568)
Total Other comprehensive (loss) income	(220)	$ (482)	$ (2)
Balance at end of period	(2,644)	(2,568)
Foreign currency translation
Other comprehensive income (loss)	254	450	(1,995)
Available-for-sale securities
Other comprehensive income (loss)	(134)	137	(5)
Cash flow hedges
Total Other comprehensive (loss) income	26	(612)	826
Accumulated Other Comprehensive Loss
Pension and other postretirement benefits
Balance at beginning of period	(2,010)	(3,611)	(3,601)
Unrecognized net actuarial loss and prior service cost/benefit	(466)	(1,112)	(478)
Tax benefit (expense)	102	380	170
Total Other comprehensive (loss) income before reclassifications, net of tax	(364)	(732)	(308)
Amortization of net actuarial loss and prior service cost/benefit	222	389	458
Tax expense	(78)	(136)	(160)
Total amount reclassified from Accumulated other comprehensive loss, net of tax	144	253	298
Total Other comprehensive (loss) income	(220)	(479)	(10)
Transfer to Alcoa Corporation	0	2,080	0
Balance at end of period	(2,230)	(2,010)	(3,611)
Foreign currency translation
Balance at beginning of period	(689)	(2,412)	(846)
Other comprehensive income (loss)	252	268	(1,566)
Transfer to Alcoa Corporation	0	1,455	0
Balance at end of period	(437)	(689)	(2,412)
Available-for-sale securities
Balance at beginning of period	132	(5)	0
Other comprehensive income (loss)	(134)	137	(5)
Transfer to Alcoa Corporation	0	0	0
Balance at end of period	(2)	132	(5)
Cash flow hedges
Balance at beginning of period	(1)	597	(230)
Net change from periodic revaluations	37	(843)	1,138
Tax benefit (expense)	(9)	252	(340)
Total Other comprehensive (loss) income before reclassifications, net of tax	28	(591)	798
Net amount reclassified to earnings	(3)	(38)	35
Tax benefit (expense)	1	12	(6)
Total amount reclassified from Accumulated other comprehensive loss, net of tax	(2)	(26)	29
Total Other comprehensive (loss) income	26	(617)	827
Transfer to Alcoa Corporation	0	19	0
Balance at end of period	25	(1)	597
Accumulated Other Comprehensive Loss | Aluminum Contracts
Cash flow hedges
Net amount reclassified to earnings	(2)	1	21
Accumulated Other Comprehensive Loss | Energy Contracts
Cash flow hedges
Net amount reclassified to earnings	0	(49)	6
Accumulated Other Comprehensive Loss | Foreign Exchange Contracts
Cash flow hedges
Net amount reclassified to earnings	0	0	5
Accumulated Other Comprehensive Loss | Interest Rate Contracts
Cash flow hedges
Net amount reclassified to earnings	0	9	1
Accumulated Other Comprehensive Loss | Nickel Contracts
Cash flow hedges
Net amount reclassified to earnings	(1)	1	2
Noncontrolling Interests
Pension and other postretirement benefits
Balance at beginning of period	0	(56)	(64)
Unrecognized net actuarial loss and prior service cost/benefit	0	(9)	5
Tax benefit (expense)	0	3	(1)
Total Other comprehensive (loss) income before reclassifications, net of tax	0	(6)	4
Amortization of net actuarial loss and prior service cost/benefit	0	4	6
Tax expense	0	(1)	(2)
Total amount reclassified from Accumulated other comprehensive loss, net of tax	0	3	4
Total Other comprehensive (loss) income	0	(3)	8
Transfer to Alcoa Corporation	0	59	0
Balance at end of period	0	0	(56)
Foreign currency translation
Balance at beginning of period	(2)	(780)	(351)
Other comprehensive income (loss)	2	182	(429)
Transfer to Alcoa Corporation	0	596	0
Balance at end of period	0	(2)	(780)
Available-for-sale securities
Balance at beginning of period	0	0	0
Other comprehensive income (loss)	0	0	0
Transfer to Alcoa Corporation	0	0	0
Balance at end of period	0	0	0
Cash flow hedges
Balance at beginning of period	0	(3)	(2)
Net change from periodic revaluations	0	36	(1)
Tax benefit (expense)	0	(10)	0
Total Other comprehensive (loss) income before reclassifications, net of tax	0	26	(1)
Net amount reclassified to earnings	0	(29)	0
Tax benefit (expense)	0	8	0
Total amount reclassified from Accumulated other comprehensive loss, net of tax	0	(21)	0
Total Other comprehensive (loss) income	0	5	(1)
Transfer to Alcoa Corporation	0	(2)	0
Balance at end of period	0	0	(3)
Noncontrolling Interests | Aluminum Contracts
Cash flow hedges
Net amount reclassified to earnings	0	0	0
Noncontrolling Interests | Energy Contracts
Cash flow hedges
Net amount reclassified to earnings	0	(34)	0
Noncontrolling Interests | Foreign Exchange Contracts
Cash flow hedges
Net amount reclassified to earnings	0	0	0
Noncontrolling Interests | Interest Rate Contracts
Cash flow hedges
Net amount reclassified to earnings	0	5	0
Noncontrolling Interests | Nickel Contracts
Cash flow hedges
Net amount reclassified to earnings	$ 0	$ 0	$ 0

Separation Transaction and Di57

Separation Transaction and Discontinued Operations - Additional Information (Detail)	Oct. 02, 2017shares	Nov. 01, 2016USD ($)agreement	Oct. 20, 2016shares	Feb. 28, 2017USD ($)shares	Sep. 30, 2014shares	May 31, 2017USD ($)investment_bank$ / sharesshares	Jun. 30, 2017USD ($)$ / sharesshares	Mar. 31, 2017USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Feb. 14, 2017$ / shares
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Investment in common stock of Alcoa Corporation									$ 0	$ 1,020,000,000
Common stock sold (in shares) | shares	24,022				25,000,000		12,958,767
Common stock sold per share (usd per share) | $ / shares							$ 35.91
Pre-tax gain on sale of common stock							$ 167,000,000		167,000,000
Proceeds from Alcoa Corporation's sale of Yadkin Hydroelectric Project									245,000,000	16,000,000	$ 25,000,000
Debt issuance and capital expenditures incurred										110,000,000
Impairment charges		$ 0							58,000,000	80,000,000	0
Selling, General Administrative, and Other Expenses
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Costs related to separation transaction, pre-tax									18,000,000	193,000,000	24,000,000
Costs related to separation transaction, after-tax									12,000,000	$ 158,000,000	$ 24,000,000
Alcoa Corporation
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Common stock outstanding percentage		80.10%
Percentage of common stock retained			19.90%
Common stock conversion ratio			0.333
Number of common stock retained (in shares) | shares			36,311,767
Common stock sold (in shares) | shares				23,353,000
Common stock sold per share (usd per share) | $ / shares												$ 38.03
Cash proceeds sale of common stock								$ 888,000,000
Pre-tax gain on sale of common stock				$ 351,000,000
Number of counterparties | investment_bank						2
Payment guarantees related to disposal group | agreement		2
Proceeds from Alcoa Corporation's sale of Yadkin Hydroelectric Project							$ 5,000,000	$ 238,000,000	$ 243,000,000
Investment Banks
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Common stock sold (in shares) | shares						12,958,767
Common stock sold per share (usd per share) | $ / shares						$ 35.91
Pre-tax gain on sale of common stock						$ 167,000,000

Separation Transaction and Di58

Separation Transaction and Discontinued Operations - Summary of Discontinued Operations in Statement of Consolidated Operations (Detail) - USD ($) $ in Millions	10 Months Ended	12 Months Ended
	Oct. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income (loss) from discontinued operations after income taxes		$ 0	$ 184	$ (41)
Less: Net income from discontinued operations attributable to noncontrolling interests		0	63	124
Net income (loss) from discontinued operations		$ 0	$ 121	(165)
Alcoa Corporation
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Sales	$ 6,752			10,121
Cost of goods sold (exclusive of expenses below)	5,655			7,965
Selling, general administrative, and other expenses	164			214
Research and development	28			69
Provision for depreciation, depletion and amortization	593			772
Restructuring and other charges	102			981
Interest expense	28			25
Other (income) expenses, net	(75)			30
Income from discontinued operations before income taxes	257			65
Provision for income taxes	73			106
Income (loss) from discontinued operations after income taxes	184			(41)
Less: Net income from discontinued operations attributable to noncontrolling interests	63			124
Net income (loss) from discontinued operations	$ 121			$ (165)

Separation Transaction and Di59

Separation Transaction and Discontinued Operations - Summary of Discontinued Operations in Statement of Consolidated Cash Flows (Detail) - Alcoa Corporation - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Depreciation, depletion and amortization	$ 593	$ 772
Restructuring and other charges	102	981
Capital expenditures	$ 298	$ 391

Restructuring and Other Charg60

Restructuring and Other Charges - Schedule of Restructuring and Other Charges (Detail) - USD ($)	Nov. 01, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restructuring and Related Activities [Abstract]
Asset impairments	$ 0	$ 58,000,000	$ 80,000,000	$ 0
Layoff costs		64,000,000	70,000,000	97,000,000
Net loss on divestitures of businesses (F)		57,000,000	3,000,000	136,000,000
Other		(3,000,000)	27,000,000	(11,000,000)
Reversals of previously recorded layoff costs		(11,000,000)	(25,000,000)	(8,000,000)
Restructuring and other charges		$ 165,000,000	$ 155,000,000	$ 214,000,000

Restructuring and Other Charg61

Restructuring and Other Charges - 2017 Actions (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)employeeposition	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	$ 165	$ 155	$ 214
Restructuring and other charges after tax	$ 143	114	192
Number of employees associated with layoff costs | position	880
Reversal of forfeited executive stock compensation	$ 13
Severance costs	64	70	97
Other exit costs
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	69	57
Restructuring and other charges after tax	47	46
Divested Businesses
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges after tax	41
Severance costs	7
Reversal Of Forfeited Executive Stock Compensation
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	(6)
Restructuring and other charges after tax and noncontrolling interests	4
Other Miscellaneous Charges
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	12	11	7
Restructuring and other charges after tax		8	4
Restructuring and other charges after tax and noncontrolling interests	7
Other Adjustments
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	(11)	25	8
Restructuring and other charges after tax		12	3
Restructuring and other charges after tax and noncontrolling interests	$ 8
Restructuring Programs Layoffs Two Thousand Seventeen
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | employee	880
Approximate number of employees already laid off | employee	300
Restructuring charges for layoffs	$ 28
Fusina Italy
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	60
Restructuring and other charges after tax and noncontrolling interests	60
Corporate
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	$ 11	$ 23	39
Number of employees associated with layoff costs | position	100
Latin America Extrusions (LAE) | Divested Businesses
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	$ 41
Engineered Products and Solutions
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | position	400
Global Rolled Products
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | position	245
Global Rolled Products | Divested Businesses
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges			136
Restructuring and other charges after tax			$ 134
Transportation and Construction Solutions
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | position	135

Restructuring and Other Charg62

Restructuring and Other Charges - 2016 Actions (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)employeeposition	Dec. 31, 2016USD ($)	Dec. 31, 2016facility	Dec. 31, 2016employee	Dec. 31, 2016position	Dec. 31, 2015USD ($)
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	$ 165	$ 155				$ 214
Restructuring and other charges after tax	$ 143	114				192
Number of employees associated with layoff costs | position	880
Layoff costs	$ 64	70				97
United Kingdom
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | employee				60
Other exit costs		4
Layoff costs		2
Tennessee | Alcoa Corporation | Toll Processing and Services Agreement
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges		21
Number of employees associated with layoff costs | position					145
Other exit costs		9
Layoff costs		7
RTI
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges		3
Restructuring and other charges after tax		2
Engineered Products and Solutions
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | position	400
Global Rolled Products
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | position	245
Transportation and Construction Solutions
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | position	135
Corporate
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	$ 11	23				39
Number of employees associated with layoff costs | position	100
Other exit costs
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	$ 69	57
Restructuring and other charges after tax	$ 47	46
Other exit costs | Tennessee | Alcoa Corporation | Toll Processing and Services Agreement
Restructuring Cost and Reserve [Line Items]
Other exit costs		2
Shutdown and Curtailment Actions
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges		37
Restructuring and other charges after tax		24
Closure Of Five Facility
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges		20
Restructuring and other charges after tax		14
Number of facilities closed | facility			5
Number of employees associated with layoff costs | position					280
Restructuring Programs Layoffs 2016
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges		53
Restructuring and other charges after tax		33
Number of employees associated with layoff costs	1,700			1,750	1,315
Approximate number of employees already laid off | employee	1,280
Restructuring charges for layoffs	$ 26	16
Restructuring Programs Layoffs 2016 | Engineered Products and Solutions
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | position					1,045
Restructuring Programs Layoffs 2016 | Global Rolled Products
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | position					30
Restructuring Programs Layoffs 2016 | Transportation and Construction Solutions
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | position					30
Restructuring Programs Layoffs 2016 | Corporate
Restructuring Cost and Reserve [Line Items]
Number of employees associated with layoff costs | position					210
Other Miscellaneous Charges
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	12	11				7
Restructuring and other charges after tax		8				4
Pension Settlement Cost
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges		2
Restructuring and other charges after tax		1
Other Adjustments
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	$ (11)	25				8
Restructuring and other charges after tax		12				$ 3
Asset Impairment and Accelerated Depreciation | United Kingdom
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges		51
Asset Retirement Obligations | Tennessee | Alcoa Corporation | Toll Processing and Services Agreement
Restructuring Cost and Reserve [Line Items]
Other exit costs		4
Environmental Remediation
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges		2
Environmental Remediation | Tennessee | Alcoa Corporation | Toll Processing and Services Agreement
Restructuring Cost and Reserve [Line Items]
Other exit costs		$ 3

Restructuring and Other Charg63

Restructuring and Other Charges - 2015 Actions (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)employee	Dec. 31, 2014divestiture
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	$ 165	$ 155	$ 214
Restructuring and other charges after tax and noncontrolling interest	143	114	192
Corporate
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	11	23	39
Divested Businesses
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges after tax and noncontrolling interest	41
Number of plant divestitures | divestiture				3
Divested Businesses | Global Rolled Products
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges			136
Restructuring and other charges after tax and noncontrolling interest			134
Restructuring Programs Layoffs Two Thousand Fourteen
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges			97
Restructuring and other charges after tax and noncontrolling interest			$ 70
Number of positions | employee			1,505
Restructuring Programs Layoffs Two Thousand Fourteen | Corporate
Restructuring Cost and Reserve [Line Items]
Number of positions | employee			400
Restructuring Programs Layoffs Two Thousand Fourteen | Global Rolled Products
Restructuring Cost and Reserve [Line Items]
Number of positions | employee			90
Restructuring Programs Layoffs Two Thousand Fourteen | Engineered Products and Solutions
Restructuring Cost and Reserve [Line Items]
Number of positions | employee			590
Restructuring Programs Layoffs Two Thousand Fourteen | Transportation and Construction Solutions
Restructuring Cost and Reserve [Line Items]
Number of positions | employee			425
Restructuring Programs Layoffs 2015
Restructuring Cost and Reserve [Line Items]
Restructuring charges for layoffs	5	55	$ 18
Shutdown and Curtailment Actions
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges		37
Restructuring and other charges after tax and noncontrolling interest		24
Shutdown and Curtailment Actions | Australia
Restructuring Cost and Reserve [Line Items]
Gain on sale of land			18
Gain on sale of land after tax			13
Other Miscellaneous Charges
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	12	11	7
Restructuring and other charges after tax and noncontrolling interest		8	4
Other Adjustments
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	$ (11)	25	8
Restructuring and other charges after tax and noncontrolling interest		$ 12	$ 3

Restructuring and Other Charg64

Restructuring and Other Charges - Schedule of Restructuring and Other Charges by Reportable Segments, Pretax (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	$ 165	$ 155	$ 214
Operating Segments
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	154	132	175
Corporate
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	11	23	39
Engineered Products and Solutions | Operating Segments
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	30	78	46
Global Rolled Products | Operating Segments
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	72	40	121
Transportation and Construction Solutions | Operating Segments
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	$ 52	$ 14	$ 8

Restructuring and Other Charg65

Restructuring and Other Charges - Activity and Reserve Balances for Restructuring Charges (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restructuring Reserve [Roll Forward]
Restructuring reserve beginning balance	$ 59	$ 93	$ 68
Cash payments	(65)	(86)	(57)
Restructuring charges	65	97	104
Other	(1)	(45)	(22)
Restructuring reserve ending balance	58	59	93
Restructuring and other charges	165	155	214
Layoff costs
Restructuring Reserve [Roll Forward]
Restructuring reserve beginning balance	50	84	48
Cash payments	(59)	(73)	(45)
Restructuring charges	64	70	97
Other	1	(31)	(16)
Restructuring reserve ending balance	56	50	84
Other exit costs
Restructuring Reserve [Roll Forward]
Restructuring reserve beginning balance	9	9	20
Cash payments	(6)	(13)	(12)
Restructuring charges	1	27	7
Other	(2)	(14)	(6)
Restructuring reserve ending balance	2	9	9
Restructuring and other charges	69	57
Stock Awards Reversal
Restructuring Reserve [Roll Forward]
Restructuring and other charges	$ 13
Other Restructuring
Restructuring Reserve [Roll Forward]
Asset retirement obligation		8
Environmental Remediation
Restructuring Reserve [Roll Forward]
Restructuring and other charges		2
Legal Costs
Restructuring Reserve [Roll Forward]
Restructuring and other charges		$ 4
Warranties Lease Terminations And Tax Indemnities
Restructuring Reserve [Roll Forward]
Restructuring and other charges			$ 5

Goodwill and Other Intangible66

Goodwill and Other Intangible Assets - Changes in Carrying Amount of Goodwill (Detail) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2017USD ($)	Dec. 31, 2017USD ($)segment	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Goodwill [Roll Forward]
Goodwill gross, beginning balance		$ 5,201	$ 5,302
Accumulated impairment losses, beginning balance		(53)	(53)
Goodwill, beginning balance		5,148	5,249
Acquisitions and Divestitures			47
Impairment		(719)	0	$ (25)
Translation and other		106	(148)
Goodwill gross, ending balance	$ 5,307	5,307	5,201	5,302
Accumulated impairment losses, ending balance	(772)	(772)	(53)	(53)
Goodwill, ending balance	4,535	$ 5,148	5,249	5,249
Number of reportable segments | segment		3
Engineered Products and Solutions
Goodwill [Roll Forward]
Impairment	(719)	$ (719)
Segment reporting, goodwill	256
Global Rolled Products
Goodwill [Roll Forward]
Segment reporting, goodwill	59
Transportation and Construction Solutions
Goodwill [Roll Forward]
Impairment				(25)
Segment reporting, goodwill	18
Operating Segments | Engineered Products and Solutions
Goodwill [Roll Forward]
Goodwill gross, beginning balance		4,579	4,660
Accumulated impairment losses, beginning balance		0	0
Goodwill, beginning balance		4,579	4,660
Acquisitions and Divestitures			47
Impairment		(719)
Translation and other		89	(128)
Goodwill gross, ending balance	4,668	4,668	4,579	4,660
Accumulated impairment losses, ending balance	(719)	(719)	0	0
Goodwill, ending balance	3,949	4,579	4,660	4,660
Operating Segments | Global Rolled Products
Goodwill [Roll Forward]
Goodwill gross, beginning balance		181	201
Accumulated impairment losses, beginning balance		0	0
Goodwill, beginning balance		181	201
Acquisitions and Divestitures			0
Impairment		0
Translation and other		12	(20)
Goodwill gross, ending balance	193	193	181	201
Accumulated impairment losses, ending balance	0	0	0	0
Goodwill, ending balance	193	181	201	201
Operating Segments | Transportation and Construction Solutions
Goodwill [Roll Forward]
Goodwill gross, beginning balance		110	111
Accumulated impairment losses, beginning balance		(53)	(53)
Goodwill, beginning balance		57	58
Acquisitions and Divestitures			0
Impairment		0
Translation and other		3	(1)
Goodwill gross, ending balance	113	113	110	111
Accumulated impairment losses, ending balance	(53)	(53)	(53)	(53)
Goodwill, ending balance	60	57	58	58
Corporate
Goodwill [Roll Forward]
Goodwill gross, beginning balance		331	330
Accumulated impairment losses, beginning balance		0	0
Goodwill, beginning balance		331	330
Acquisitions and Divestitures			0
Impairment		0
Translation and other		2	1
Goodwill gross, ending balance	333	333	331	330
Accumulated impairment losses, ending balance	0	0	0	0
Goodwill, ending balance	$ 333	$ 331	$ 330	$ 330

Goodwill and Other Intangible67

Goodwill and Other Intangible Assets - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Goodwill [Line Items]
Goodwill impairment		$ 719	$ 0	$ 25
Amortization of intangible assets		71	$ 65	67
Engineered Products and Solutions
Goodwill [Line Items]
Goodwill impairment	$ 719	719
Transportation and Construction Solutions
Goodwill [Line Items]
Goodwill impairment				$ 25
Minimum
Goodwill [Line Items]
Expected amortization for the year 2018	60	60
Expected amortization for the year 2019	60	60
Expected amortization for the year 2020	60	60
Expected amortization for the year 2021	60	60
Expected amortization for the year 2022	60	60
Maximum
Goodwill [Line Items]
Expected amortization for the year 2018	75	75
Expected amortization for the year 2019	75	75
Expected amortization for the year 2020	75	75
Expected amortization for the year 2021	75	75
Expected amortization for the year 2022	$ 75	$ 75

Goodwill and Other Intangible68

Goodwill and Other Intangible Assets - Other Intangible Assets (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	$ 1,852	$ 1,762
Accumulated amortization	(897)	(806)
Indefinite-lived trade names and trademarks	32	32
Total other intangible assets	1,884	1,794
Computer software
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	789	755
Accumulated amortization	(674)	(623)
Patents and licenses
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	110	110
Accumulated amortization	(107)	(102)
Other intangible assets
Finite-Lived Intangible Assets [Line Items]
Gross carrying amount	953	897
Accumulated amortization	$ (116)	$ (81)

Acquisitions and Divestitures -

Acquisitions and Divestitures - 2017 Divestitures (Details) $ in Millions	1 Months Ended		3 Months Ended								12 Months Ended
	Dec. 31, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2017USD ($)	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Sep. 30, 2016USD ($)	Jun. 30, 2016USD ($)	Mar. 31, 2016USD ($)	Dec. 31, 2017USD ($)employee	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Business Acquisition [Line Items]
Net loss on divestitures of businesses											$ 57	$ 3	$ 136
Sales revenue, goods, net			$ 3,271	$ 3,236	$ 3,261	$ 3,192	$ 2,967	$ 3,138	$ 3,234	$ 3,055	12,960	12,394	12,413
Restructuring and other charges											165	155	$ 214
Slim Aluminium
Business Acquisition [Line Items]
Cash expense related to divestiture of business		$ 10
Guarantee payments to third party		$ 5
Sales revenue, goods, net											$ 54	$ 165
Number of employees | employee											312
Slim Aluminium | Restructuring and Other Charges
Business Acquisition [Line Items]
Net loss on divestitures of businesses											$ 60
Latin America Extrusions (LAE)
Business Acquisition [Line Items]
Proceeds from divestiture of businesses	$ 10
Latin America Extrusions (LAE) | Divested Businesses
Business Acquisition [Line Items]
Restructuring and other charges			$ 41

Acquisitions and Divestitures70

Acquisitions and Divestitures - 2016 Divestitures (Details)

1 Months Ended

3 Months Ended

4 Months Ended

5 Months Ended

12 Months Ended

Apr. 30, 2016USD ($)

Dec. 31, 2017USD ($)

Sep. 30, 2017USD ($)

Jun. 30, 2017USD ($)

Mar. 31, 2017USD ($)

Dec. 31, 2016USD ($)

Sep. 30, 2016USD ($)

Jun. 30, 2016USD ($)

Mar. 31, 2016USD ($)

Apr. 29, 2016USD ($)employee

Dec. 31, 2015USD ($)

Dec. 31, 2017USD ($)

Dec. 31, 2016USD ($)

Dec. 31, 2015USD ($)

Business Acquisition [Line Items]

Disposal group, deferred gain on disposal

$ 0

Sales revenue, goods, net

$ 3,271,000,000

$ 3,236,000,000

$ 3,261,000,000

$ 3,192,000,000

$ 2,967,000,000

$ 3,138,000,000

$ 3,234,000,000

$ 3,055,000,000

$ 12,960,000,000

$ 12,394,000,000

$ 12,413,000,000

LISI MEDICAL

Business Acquisition [Line Items]

Proceeds from divestiture of businesses

102,000,000

Proceeds from divestiture of businesses net of transaction costs

99,000,000

RTI

Business Acquisition [Line Items]

Sales revenue, goods, net

$ 20,000,000

$ 309,000,000

Number of employees | employee

330

Goodwill

Business Acquisition [Line Items]

Increase (decrease) intangible assets

$ (44,000,000)

Acquisitions and Divestitures71

Acquisitions and Divestitures - 2015 Acquisitions (Detail) $ / shares in Units, € in Millions	Oct. 05, 2016shares	Jul. 23, 2015shares	Jul. 22, 2015shares	Jul. 31, 2015USD ($)$ / sharesshares	Mar. 31, 2015USD ($)employee	Mar. 31, 2015EUR (€)employee	Dec. 31, 2017USD ($)$ / shares	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)$ / shares	Mar. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Sep. 30, 2016USD ($)	Jun. 30, 2016USD ($)	Mar. 31, 2016USD ($)	Apr. 29, 2016USD ($)employee	Dec. 31, 2015USD ($)	Dec. 31, 2017USD ($)$ / sharesshares	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)Tranchecompany	Dec. 31, 2014USD ($)employee	Oct. 04, 2016shares	Sep. 30, 2015USD ($)	Sep. 30, 2015EUR (€)	Mar. 06, 2015$ / shares
Business Acquisition [Line Items]
Goodwill							$ 4,535,000,000				$ 5,148,000,000					$ 5,249,000,000	$ 4,535,000,000	$ 5,148,000,000	$ 5,249,000,000
Common stock conversion transaction value							0				0					870,000,000	0	0	870,000,000
Common stock sold per share (usd per share) | $ / shares									$ 35.91
Sales revenue, goods, net							$ 3,271,000,000	$ 3,236,000,000	$ 3,261,000,000	$ 3,192,000,000	$ 2,967,000,000	$ 3,138,000,000	$ 3,234,000,000	$ 3,055,000,000			12,960,000,000	12,394,000,000	12,413,000,000
Adjusted EBITDA																	$ 2,144,000,000	$ 2,063,000,000	1,894,000,000
TITAL
Business Acquisition [Line Items]
Cash paid for business acquisition					$ 204,000,000	€ 188
Business acquisition transaction cost																						$ 1,000,000	€ 1
Number of employees | employee					650	650
Goodwill					$ 118,000,000									117,000,000
Goodwill, purchase accounting adjustments														$ 1,000,000
RTI
Business Acquisition [Line Items]
Number of employees | employee															330
Goodwill																298,000,000			298,000,000
Goodwill deductible for income tax purpose					$ 0											0			$ 0
Common stock conversion transaction value				$ 870,000,000
Common stock sold per share (usd per share) | $ / shares				$ 9.96																				$ 14.48
Debt instrument, convertible, conversion price | $ / shares				$ 2.8315
Number of common stock shares issued in a part of acquisition (in shares) | shares	29,000,000	87,397,414	29,132,471	29,132,471																	87,000,000
Acquisition price per share (USD per share) | $ / shares																								$ 41
Professional fees and costs				$ 25,000,000
Professional fees and costs, after tax				$ 19,000,000
Sales revenue, goods, net															$ 20,000,000	309,000,000
Synergy from merger and acquisition, number of companies | company																			2
RTI | Convertible Notes
Business Acquisition [Line Items]
Debt instrument, convertible, conversion price | $ / shares				$ 28.1596
Number of repayment tranches | Tranche																			2
Debt instrument, amount received upon maturity per one thousand dollars in principal amount of notes held				$ 1,000
RTI | Tranche Due December 2015
Business Acquisition [Line Items]
Long-term debt due within one year				115,000,000
RTI | Tranche Due October 2019
Business Acquisition [Line Items]
Long-term debt due within one year				$ 403,000,000												403,000,000			$ 403,000,000
RTI | 1.63% Convertible Notes, Due 2019 | Convertible Notes
Business Acquisition [Line Items]
Debt instrument, convertible, conversion price | $ / shares							$ 28.1596										$ 28.1596
Conversion of notes to common stock (in shares) | shares																	14,294,000
Debt instrument, convertible, conversion rate per bond							0.0355119										0.0355119
RTI | Customer Relationships
Business Acquisition [Line Items]
Finite-lived intangible assets acquired																			$ 37,000,000
Weighted average amortization period of intangible asset																			20 years
Maximum | RTI
Business Acquisition [Line Items]
Adjusted EBITDA																$ 21,000,000
RTI
Business Acquisition [Line Items]
Number of employees | employee																				2,600
Sales revenue, goods, net																				$ 794,000,000

Acquisitions and Divestitures72

Acquisitions and Divestitures - 2015 Divestiture (Detail) $ in Millions	1 Months Ended	12 Months Ended
	Mar. 31, 2015USD ($)employee	Dec. 31, 2015USD ($)
Stupino Titanium Company
Business Acquisition [Line Items]
Sale generated in last annual period prior to divestiture	$ 130
Number of employees | employee	1,870
Russia
Business Acquisition [Line Items]
Net cash received		$ 11
Loss from divestitures before income tax		$ (137)

Acquisitions and Divestitures73

Acquisitions and Divestitures - 2014 Acquisitions (Detail) - Firth Rixson - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Nov. 30, 2014
Business Acquisition [Line Items]
Contingent consideration liability	$ 0		$ 0
Contingent consideration arrangements, change in amount of contingent consideration, liability	$ 81	$ 56	$ (81)	$ (56)
Maximum
Business Acquisition [Line Items]
Contingent consideration liability					$ 150

Inventories - Schedule of Inven

Inventories - Schedule of Inventory Components (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Inventory Disclosure [Abstract]
Finished goods	$ 669	$ 625
Work-in-process	1,349	1,144
Purchased raw materials	381	408
Operating supplies	81	76
Inventories, total	$ 2,480	$ 2,253

Inventories - Additional Inform

Inventories - Additional Information (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Inventory Disclosure [Abstract]
Inventories valued on a LIFO basis	$ 1,208	$ 947
Total inventories valued on an average-cost basis	$ 481	$ 371

Properties, Plants, and Equip76

Properties, Plants, and Equipment, Net - Schedule of Properties, Plants, and Equipment, Net (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Properties, plants, and equipment, gross	$ 11,365	$ 10,789
Less: accumulated depreciation and amortization	6,392	6,073
Properties, plants, and equipment excluding construction work-in-progress	4,973	4,716
Construction work-in-progress	621	783
Properties, plants, and equipment, net	5,594	5,499
Land and Land Rights
Property, Plant and Equipment [Line Items]
Properties, plants, and equipment, gross	140	135
Structures
Property, Plant and Equipment [Line Items]
Properties, plants, and equipment, gross	2,395	2,296
Machinery and equipment
Property, Plant and Equipment [Line Items]
Properties, plants, and equipment, gross	8,830	8,358
Operating Segments | Engineered Products and Solutions | Structures
Property, Plant and Equipment [Line Items]
Properties, plants, and equipment, gross	784	733
Operating Segments | Engineered Products and Solutions | Machinery and equipment
Property, Plant and Equipment [Line Items]
Properties, plants, and equipment, gross	3,054	2,728
Operating Segments | Global Rolled Products | Structures
Property, Plant and Equipment [Line Items]
Properties, plants, and equipment, gross	1,090	1,061
Operating Segments | Global Rolled Products | Machinery and equipment
Property, Plant and Equipment [Line Items]
Properties, plants, and equipment, gross	4,641	4,570
Operating Segments | Transportation and Construction Solutions | Structures
Property, Plant and Equipment [Line Items]
Properties, plants, and equipment, gross	268	254
Operating Segments | Transportation and Construction Solutions | Machinery and equipment
Property, Plant and Equipment [Line Items]
Properties, plants, and equipment, gross	777	723
Other
Property, Plant and Equipment [Line Items]
Properties, plants, and equipment, net	310	308
Other | Structures
Property, Plant and Equipment [Line Items]
Properties, plants, and equipment, gross	253	248
Other | Machinery and equipment
Property, Plant and Equipment [Line Items]
Properties, plants, and equipment, gross	$ 358	$ 337

Debt - Schedule of Long-Term De

Debt - Schedule of Long-Term Debt (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Long-term debt	$ 6,807	$ 8,048
Less: amount due within one year	1	4
Long-term debt, excluding amount due within one year	6,806	$ 8,044
6.50% Bonds, due 2018
Debt Instrument [Line Items]
Convertible notes, interest rate		6.50%
Long-term debt	0	$ 250
6.75% Notes, due 2018
Debt Instrument [Line Items]
Convertible notes, interest rate		6.75%
Long-term debt	$ 0	$ 750
5.72% Notes, due 2019
Debt Instrument [Line Items]
Convertible notes, interest rate	5.72%
Long-term debt	$ 500	750
1.63% Convertible Notes, Due 2019
Debt Instrument [Line Items]
Convertible notes, interest rate	1.63%
Long-term debt	$ 403	403
6.150% Notes, due 2020
Debt Instrument [Line Items]
Convertible notes, interest rate	6.15%
Long-term debt	$ 1,000	1,000
5.40% Notes, due 2021
Debt Instrument [Line Items]
Convertible notes, interest rate	5.40%
Long-term debt	$ 1,250	1,250
5.87% Notes, due 2022
Debt Instrument [Line Items]
Convertible notes, interest rate	5.87%
Long-term debt	$ 627	627
5.125% Notes, due 2024
Debt Instrument [Line Items]
Convertible notes, interest rate	5.125%
Long-term debt	$ 1,250	1,250
5.90% Notes, due 2027
Debt Instrument [Line Items]
Convertible notes, interest rate	5.90%
Long-term debt	$ 625	625
6.75% Bonds, due 2028
Debt Instrument [Line Items]
Convertible notes, interest rate	6.75%
Long-term debt	$ 300	300
5.95% Notes due 2037
Debt Instrument [Line Items]
Convertible notes, interest rate	5.95%
Long-term debt	$ 625	625
Iowa Finance Authority Loan, due 2042 (4.75%)
Debt Instrument [Line Items]
Convertible notes, interest rate	4.75%
Long-term debt	$ 250	250
Other
Debt Instrument [Line Items]
Other	$ (23)	$ (32)

Debt - Maturities of Long-term

Debt - Maturities of Long-term Debt (Detail) $ in Millions	Dec. 31, 2017USD ($)
Debt Disclosure [Abstract]
Principal amount of long-term debt maturing in year 2018	$ 1
Principal amount of long-term debt maturing in year 2019	903
Principal amount of long-term debt maturing in year 2020	1,000
Principal amount of long-term debt maturing in year 2021	1,250
Principal amount of long-term debt maturing in year 2022	$ 627

Debt (Public Debt) (Detail)

Debt (Public Debt) (Detail)	Oct. 02, 2017shares	Jun. 19, 2017USD ($)	Dec. 31, 2016USD ($)	Sep. 30, 2014shares	May 31, 2017USD ($)$ / sharesshares	Jun. 30, 2017USD ($)$ / sharesshares	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Apr. 30, 2017USD ($)cash_tender_offer
Debt Instrument [Line Items]
Cash paid to holders of debt instrument, net						$ 409,000,000
Common stock sold (in shares) | shares	24,022			25,000,000		12,958,767
Common stock sold per share (usd per share) | $ / shares						$ 35.91
Debt instrument, repurchase amount						$ 874,000,000
Interest expense, debt						58,000,000
Interest paid						27,000,000
Legal fees						2,000,000
Pre-tax gain on sale of common stock						167,000,000	$ 167,000,000
Interest expense (S)		$ 24,000,000					496,000,000	$ 499,000,000	$ 473,000,000
Principal amount of convertible notes			$ 8,048,000,000				6,807,000,000	$ 8,048,000,000
6.50% Bonds, due 2018
Debt Instrument [Line Items]
Convertible notes, interest rate			6.50%					6.50%
Principal amount of convertible notes			$ 250,000,000				0	$ 250,000,000
6.75% Notes, due 2018
Debt Instrument [Line Items]
Convertible notes, interest rate			6.75%					6.75%
Principal amount of convertible notes			$ 750,000,000				$ 0	$ 750,000,000
5.72% Notes, due 2019
Debt Instrument [Line Items]
Convertible notes, interest rate							5.72%
Principal amount of convertible notes			$ 750,000,000				$ 500,000,000	$ 750,000,000
6.5% Senior Notes Due 2018
Debt Instrument [Line Items]
Debt instrument, face amount		100,000,000
6.75% Senior Notes Due 2018
Debt Instrument [Line Items]
Debt instrument, face amount		345,000,000
Debt instrument redemption amount		$ 479,000,000
5.55% Notes Due February 2017
Debt Instrument [Line Items]
Convertible notes, interest rate			5.55%					5.55%
Cash paid to holders of debt instrument, net			$ 770,000,000
Principal amount of convertible notes			750,000,000					$ 750,000,000
Cash paid to holders of debt instrument, portion of interest			17,000,000
Cash paid to holders of debt instrument, portion of purchase premium			$ 3,000,000
Investment Banks
Debt Instrument [Line Items]
Number of cash tender offers | cash_tender_offer										3
Debt instrument, face amount										$ 805,000,000
Common stock sold (in shares) | shares					12,958,767
Common stock sold per share (usd per share) | $ / shares					$ 35.91
Pre-tax gain on sale of common stock					$ 167,000,000
Investment Banks | 6.50% Bonds, due 2018
Debt Instrument [Line Items]
Debt instrument, face amount										150,000,000
Investment Banks | 6.75% Notes, due 2018
Debt Instrument [Line Items]
Debt instrument, face amount										405,000,000
Investment Banks | 5.72% Notes, due 2019
Debt Instrument [Line Items]
Debt instrument, face amount										250,000,000
Interest Rate Swap
Debt Instrument [Line Items]
Proceeds from interest received						$ 8,000,000
Maximum | Investment Banks
Debt Instrument [Line Items]
Debt instrument, face amount										$ 1,000,000,000

Debt (Credit Facilities) (Detai

Debt (Credit Facilities) (Detail) - USD ($)	Jul. 25, 2014	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Sep. 30, 2016
Debt Instrument [Line Items]
Ratio of indebtedness to consolidated EBITDA		4.50%
Ratio of indebtedness to consolidated EBITDA, after December 31, 2019		3.50%
Extension of maturity period		1 year
Maximum borrowing capacity		$ 715,000,000
Arconic
Debt Instrument [Line Items]
Line of credit facility, repayment		$ 810,000,000	$ 1,950,000,000	$ 1,890,000,000
Weighted-average interest rate		2.60%	1.90%	1.60%
Weighted-average maturity days		46 days	49 days	69 days
Maximum
Debt Instrument [Line Items]
Applicable margin on LIBOR loans		1.70%
Minimum
Debt Instrument [Line Items]
Applicable margin on LIBOR loans		0.70%
Revolving Credit Agreement
Debt Instrument [Line Items]
Revolving credit facility, term	5 years
Revolving Credit Agreement | Prior to Amendment
Debt Instrument [Line Items]
Line of credit facility, outstanding borrowings	$ 4,000,000,000
Revolving Credit Agreement | After Amendment
Debt Instrument [Line Items]
Line of credit facility, outstanding borrowings					$ 3,000,000,000
Commercial Paper | Maximum
Debt Instrument [Line Items]
Fees paid to maintain credit facility		0.30%
Senior Unsecured Revolving Credit Facility
Debt Instrument [Line Items]
Line of credit facility, outstanding borrowings		$ 0	$ 0
Amounts borrowed under the credit agreement		0	$ 0	$ 0
Expected Maturity Date Year 2017
Debt Instrument [Line Items]
Maximum borrowing capacity		640,000,000
Expected Maturity Date Year 2018
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 75,000,000

Debt (Short-Term Borrowings) (D

Debt (Short-Term Borrowings) (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Debt Disclosure [Abstract]
Short-term debt (I and U)	$ 38	$ 40
Accounts payable settlement arrangements	$ 33	$ 31

Debt (Commercial Paper) (Detail

Debt (Commercial Paper) (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Average outstanding commercial paper	$ 67,000,000	$ 127,000,000
Long-term interest rate	1.60%	1.10%	0.60%
Commercial Paper
Debt Instrument [Line Items]
Aggregate outstanding principal amount	$ 0	$ 0
Debt instrument maturity date, description	1 year

Other Noncurrent Liabilities 83

Other Noncurrent Liabilities and Deferred Credits - Schedule of Other Noncurrent Liabilities and Deferred Credits (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Payables and Accruals [Abstract]
Environmental remediation (L)	$ 253	$ 260
Income taxes (Q)	162	154
Accrued compensation and retirement costs	218	216
Contingent payment related to an acquisition (F)	0	78
Other	126	162
Other noncurrent liabilities and deferred credits	$ 759	$ 870

Contingencies and Commitments -

Contingencies and Commitments - Contingencies (Detail) € in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)location	Dec. 31, 2017EUR (€)	Dec. 31, 2016USD ($)
Loss Contingencies [Line Items]
Number of cleanup locations (more than) | location	100
Remediation reserve balance	$ 294		$ 308
Remediation reserve balance, classified as a current liability	41		48
Increase in remediation reserve	5
Accrual for environmental loss contingencies, revision in estimates	8
Increase (decrease) in reserves due to effects of foreign currency translation	1
Payments related to remediation expenses applied against the reserve	$ 26
Actual remediation fieldwork period	4 years
Total combined assessments	$ 155	€ 130
Massena West, NY
Loss Contingencies [Line Items]
Remediation reserve balance	$ 215		$ 228
Recurring Costs of Managing Hazardous Substances and Environmental Programs | Maximum
Loss Contingencies [Line Items]
Percentage of cost of goods sold	1.00%

Contingencies and Commitments85

Contingencies and Commitments - Commitments (Detail)	3 Months Ended	12 Months Ended
	Dec. 31, 2017USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)agreementguarantee	Dec. 31, 2015USD ($)	Nov. 01, 2016USD ($)
Loss Contingencies [Line Items]
Purchase obligations due in 2018	$ 861,000,000	$ 861,000,000
Purchase obligations due in 2019	176,000,000	176,000,000
Purchase obligations due in 2020	74,000,000	74,000,000
Purchase obligations due in 2021	13,000,000	13,000,000
Purchase obligations due in 2022	6,000,000	6,000,000
Purchase obligations due thereafter	5,000,000	5,000,000
Operating leases, expense		113,000,000	$ 110,000,000	$ 112,000,000
Long-term operating leases, minimum annual rentals due in 2018	108,000,000	108,000,000
Long-term operating leases, minimum annual rentals due in 2019	88,000,000	88,000,000
Long-term operating leases, minimum annual rentals due in 2020	62,000,000	62,000,000
Long-term operating leases, minimum annual rentals due in 2021	46,000,000	46,000,000
Long-term operating leases, minimum annual rentals due in 2022	38,000,000	38,000,000
Long-term operating leases, minimum annual rentals due thereafter	100,000,000	100,000,000
Guarantees of third party related to project financing	29,000,000	29,000,000
Other income, net		640,000,000	94,000,000	$ 28,000,000
Letters of credit, total amount committed	120,000,000	120,000,000
Total amount committed under outstanding surety bonds	54,000,000	54,000,000
Other Noncurrent Liabilities and Deferred Credits
Loss Contingencies [Line Items]
Combined fair value of guarantees	8,000,000	8,000,000	35,000,000
Separation Agreement
Loss Contingencies [Line Items]
Guarantees of third party related to project financing	197,000,000	197,000,000	354,000,000
Other income, net	25,000,000
Combined fair value of guarantees	1,297,000,000	1,297,000,000
Total amount committed under outstanding surety bonds	$ 25,000,000	$ 25,000,000			$ 25,000,000
Alcoa Corporation Energy Supply Contracts Guarantee
Loss Contingencies [Line Items]
Guarantees of third party related to project financing			$ 50,000,000
Guarantor obligations, number of contracts | guarantee			2
Alcoa Corporation Environmental Liabilities Guarantee
Loss Contingencies [Line Items]
Guarantees of third party related to project financing			$ 53,000,000
Purchase Agreement
Loss Contingencies [Line Items]
Long-term purchase commitment, period			1 year
Guarantees of third party related to project financing			$ 245,000,000
Number of long term energy supply agreements | agreement			2
Alcoa Corporation Workers Compensation Claims
Loss Contingencies [Line Items]
Letters of credit, total amount committed					62,000,000
Alcoa Corporation Equipment Leases And Energy Contracts
Loss Contingencies [Line Items]
Letters of credit, total amount committed					$ 103,000,000

Other Income, Net - Schedule of

Other Income, Net - Schedule of Other Expenses (Income), Net (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other Income and Expenses [Abstract]
Equity income	$ 0	$ (7)	$ 0
Interest income	(19)	(16)	(16)
Foreign currency (gains) losses, net	(5)	(4)	51
Net (gain) loss from asset sales	(513)	11	(42)
Net loss (gain) on mark-to-market derivative contracts	0	1	(3)
Other, net	(103)	(79)	(18)
Other income, net	$ (640)	$ (94)	$ (28)

Other Income, Net - Additional

Other Income, Net - Additional Information (Detail) - USD ($) $ in Millions	1 Months Ended	3 Months Ended			12 Months Ended
	Feb. 28, 2017	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Nov. 01, 2016
Other Non operating Income Expense [Line Items]
Net loss (gain) from asset sales					$ 513	$ 156	$ 74
Pre-tax gain on sale of common stock			$ 167		167
Total amount committed under outstanding surety bonds		$ 54			54
Other, net					103	79	18
Firth Rixson
Other Non operating Income Expense [Line Items]
Contingent consideration arrangements, change in amount of contingent consideration, liability		(81)		$ (56)	81	56
Business combination, post acquisition closing adjustment						$ (20)
Separation Agreement
Other Non operating Income Expense [Line Items]
Total amount committed under outstanding surety bonds		$ 25			25			$ 25
Alcoa Corporation
Other Non operating Income Expense [Line Items]
Net loss (gain) from asset sales					$ 351
Pre-tax gain on sale of common stock	$ 351
Sherwin, TX Site
Other Non operating Income Expense [Line Items]
Net loss (gain) from asset sales							19
China Rolling Mill Equity Investment
Other Non operating Income Expense [Line Items]
Net loss (gain) from asset sales							$ 19

Cash Flow Information - Schedul

Cash Flow Information - Schedule of Cash Paid for Interest and Income Taxes (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplemental Cash Flow Information [Abstract]
Interest, net of amount capitalized	$ 508	$ 524	$ 487
Income taxes, net of amount refunded	$ 118	$ 324	$ 345

Cash Flow Information - Sched89

Cash Flow Information - Schedule of Cash Paid for Acquisitions Including Non-Controlling Interest (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplemental Cash Flow Information [Abstract]
Assets acquired	$ 0	$ 0	$ 2,003
Liabilities assumed	0	0	(868)
Equity issued	0	0	(870)
Working capital adjustment	0	(10)	0
Increase in Arconic’s shareholders’ equity	0	0	(60)
Cash paid	0	(10)	205
Less: cash acquired	0	0	302
Net cash paid	$ 0	$ (10)	$ (97)

Cash Flow Information - Additio

Cash Flow Information - Additional Information (Detail) $ / shares in Units, $ in Millions	Oct. 02, 2017$ / sharesshares	Oct. 05, 2016$ / sharesshares	Aug. 31, 2016shares	Jul. 23, 2015shares	Jul. 22, 2015shares	Aug. 31, 2016shares	Aug. 31, 2016USD ($)shares	Aug. 30, 2016USD ($)	Jul. 31, 2015USD ($)shares	Sep. 30, 2014shares	Jun. 30, 2017USD ($)shares	Dec. 31, 2017USD ($)shares	Dec. 31, 2016USD ($)shares	Dec. 31, 2015USD ($)shares	Oct. 04, 2016shares	Dec. 31, 2014shares
Schedule Of Common Stock [Line Items]
Sales of investments												$ 890	$ 280	$ 40
Proceeds from sale of company-owned life insurance policies													457
Proceeds from Divestiture of Businesses												$ (9)	$ 692	$ 112
Depository shares sold (in shares) | shares	24,022									25,000,000	12,958,767
Interest in preferred stock	0.10									0.10
Conversion of stock, shares converted (in shares) | shares	31,420
Reverse stock split ratio		0.3333
Common stock share outstanding (in shares) | shares		400,000,000										481,416,537	438,519,780	1,310,160,141	1,300,000,000	1,216,663,661
Common stock par value (usd per share) | $ / shares		$ 1
Decrease in common stock due to reverse stock split													$ (877)
Treasury stock retirement (in shares) | shares			25,000,000			76,000,000	76,000,000
Retirement of treasury stock								$ 76					0
Increase in additional paid in capital due to reverse stock split													877
Common stock conversion transaction value												$ 0	0	$ 870
Common stock
Schedule Of Common Stock [Line Items]
Retirement of treasury stock							$ 76	76					76
Number of common stock shares issued in a part of acquisition (in shares) | shares														87,397,414
Additional capital
Schedule Of Common Stock [Line Items]
Retirement of treasury stock							$ 2,563	$ 2,563					2,563
RTI
Schedule Of Common Stock [Line Items]
Common stock conversion transaction value									$ 870
Number of common stock shares issued in a part of acquisition (in shares) | shares		29,000,000		87,397,414	29,132,471				29,132,471						87,000,000
Remmele Medical
Schedule Of Common Stock [Line Items]
Proceeds from Divestiture of Businesses													(102)
Alcoa Corporation
Schedule Of Common Stock [Line Items]
Sales of investments													145
Proceeds from Divestiture of Businesses													120
Alcoa Corporation | Electricity Contract
Schedule Of Common Stock [Line Items]
Outstanding notes held by Investment banks, including accrued and unpaid interest											$ 465
Mandatory convertible preferred stock
Schedule Of Common Stock [Line Items]
Depository shares sold (in shares) | shares	24,975,978
Interest in preferred stock	0.1
Preferred stock conversion price (in usd per share) | $ / shares	$ 1.56996
Conversion of stock, shares converted (in shares) | shares	39,211,286
Exchange Traded Fixed Income and Equity Securities
Schedule Of Common Stock [Line Items]
Sales of investments													$ 130

Segment and Geographic Area I91

Segment and Geographic Area Information - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2017segment
Segment Reporting Information [Line Items]
Number of reportable segments	3
Sales Revenue, Segment | Product Concentration Risk
Segment Reporting Information [Line Items]
Sales percentage	75.00%

Segment and Geographic Area I92

Segment and Geographic Area Information - Schedule of Operating Results of Arconic's Reportable Segment (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Total sales	$ 3,271	$ 3,236	$ 3,261	$ 3,192	$ 2,967	$ 3,138	$ 3,234	$ 3,055	$ 12,960	$ 12,394	$ 12,413
Depreciation and amortization									523	504	479
Adjusted EBITDA									2,144	2,063	1,894
Capital expenditures									543	689
Goodwill	4,202				4,817				4,202	4,817
Total assets	15,499				15,415				15,499	15,415
Operating Segments
Segment Reporting Information [Line Items]
Total sales									13,060	12,512	12,602
Intersegment Eliminations
Segment Reporting Information [Line Items]
Intersegment sales									148	118	125
Total sales									(148)	(118)	(125)
Third-Party Sales | Operating Segments
Segment Reporting Information [Line Items]
Segment Reporting Information Revenues From External Customers									12,912	12,394	12,477
Engineered Products and Solutions
Segment Reporting Information [Line Items]
Depreciation and amortization									268	255	233
Adjusted EBITDA									1,224	1,195	1,111
Capital expenditures									308	333
Goodwill	3,949				4,579				3,949	4,579
Total assets	10,252				10,542				10,252	10,542
Engineered Products and Solutions | Operating Segments
Segment Reporting Information [Line Items]
Total sales									5,935	5,728	5,342
Engineered Products and Solutions | Intersegment Eliminations
Segment Reporting Information [Line Items]
Intersegment sales									0	0	0
Engineered Products and Solutions | Third-Party Sales | Operating Segments
Segment Reporting Information [Line Items]
Segment Reporting Information Revenues From External Customers									5,935	5,728	5,342
Global Rolled Products
Segment Reporting Information [Line Items]
Depreciation and amortization									205	201	203
Adjusted EBITDA									599	577	512
Capital expenditures									178	293
Goodwill	193				181				193	181
Total assets	4,179				3,891				4,179	3,891
Global Rolled Products | Operating Segments
Segment Reporting Information [Line Items]
Total sales									5,140	4,982	5,378
Global Rolled Products | Intersegment Eliminations
Segment Reporting Information [Line Items]
Intersegment sales									148	118	125
Global Rolled Products | Third-Party Sales | Operating Segments
Segment Reporting Information [Line Items]
Segment Reporting Information Revenues From External Customers									4,992	4,864	5,253
Transportation and Construction Solutions
Segment Reporting Information [Line Items]
Depreciation and amortization									50	48	43
Adjusted EBITDA									321	291	271
Capital expenditures									57	63
Goodwill	60				57				60	57
Total assets	$ 1,068				$ 982				1,068	982
Transportation and Construction Solutions | Operating Segments
Segment Reporting Information [Line Items]
Total sales									1,985	1,802	1,882
Transportation and Construction Solutions | Intersegment Eliminations
Segment Reporting Information [Line Items]
Intersegment sales									0	0	0
Transportation and Construction Solutions | Third-Party Sales | Operating Segments
Segment Reporting Information [Line Items]
Segment Reporting Information Revenues From External Customers									$ 1,985	$ 1,802	$ 1,882

Segment and Geographic Area I93

Segment and Geographic Area Information - Schedule of Reconciliation of Certain Segment Information to Consolidated Totals (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting, Revenue Reconciling Item [Line Items]
Sales revenue, goods, net	$ 3,271	$ 3,236	$ 3,261	$ 3,192	$ 2,967	$ 3,138	$ 3,234	$ 3,055	$ 12,960	$ 12,394	$ 12,413
Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Sales revenue, goods, net									13,060	12,512	12,602
Intersegment Eliminations
Segment Reporting, Revenue Reconciling Item [Line Items]
Sales revenue, goods, net									(148)	(118)	(125)
Corporate
Segment Reporting, Revenue Reconciling Item [Line Items]
Sales revenue, goods, net									$ 48	$ 0	$ (64)

Segment and Geographic Area I94

Segment and Geographic Area Information - Schedule of Segment EBITDA to Consolidated Net (Loss) Income Attributable to Arconic (Detail) - USD ($) $ in Millions	Jun. 19, 2017	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Combined segment adjusted EBITDA										$ 2,144	$ 2,063	$ 1,894
Impairment of goodwill										(719)	0	(25)
Restructuring and other charges										(165)	(155)	(214)
Operating income										326	819	628
Interest expense	$ (24)									(496)	(499)	(473)
Other income, net										640	94	28
Income from continuing operations before income taxes										470	414	183
Provision for income taxes										(544)	(1,476)	(339)
Discontinued operations										0	121	(165)
Net loss attributable to Arconic		$ (727)	$ 119	$ 212	$ 322	$ (1,258)	$ 166	$ 135	$ 16	(74)	(941)	(322)
Other
Segment Reporting Information [Line Items]
Depreciation and amortization										(551)	(535)	(508)
Impairment of goodwill										(719)	0	(25)
Restructuring and other charges										(165)	(155)	(214)
Impact of LIFO										(110)	(18)	101
Metal price lag										72	27	(175)
Corporate expense										(274)	(454)	(371)
Other										(71)	(109)	(74)
Operating income										326	819	628
Interest expense										(496)	(499)	(473)
Other income, net										640	94	28
Income from continuing operations before income taxes										470	414	183
Provision for income taxes										(544)	(1,476)	(339)
Discontinued operations										0	121	(165)
Net income attributable to noncontrolling interest										$ 0	$ 0	$ (1)

Segment and Geographic Area I95

Segment and Geographic Area Information - Schedule of Segment Reporting Information to Consolidated Assets (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule Of Assets By Segment [Line Items]
Total assets	$ 18,718	$ 20,038
Cash and cash equivalents	2,150	1,863	$ 1,919	$ 1,877
Corporate goodwill	4,535	5,148	$ 5,249
Corporate fixed assets, net	5,594	5,499
LIFO reserve	481	371
Investment in common stock of Alcoa Corporation	0	1,020
Operating Segments
Schedule Of Assets By Segment [Line Items]
Total assets	15,499	15,415
Other
Schedule Of Assets By Segment [Line Items]
Cash and cash equivalents	2,150	1,863
Deferred income taxes	743	1,234
Corporate goodwill	333	331
Corporate fixed assets, net	310	308
LIFO reserve	(481)	(371)
Fair value of derivative contracts	91	24
Investment in common stock of Alcoa Corporation	0	1,020
Other	$ 73	$ 214

Segment and Geographic Area I96

Segment and Geographic Area Information - Sales by Major Product Grouping (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Product Information [Line Items]
Sales revenue, goods, net	$ 3,271	$ 3,236	$ 3,261	$ 3,192	$ 2,967	$ 3,138	$ 3,234	$ 3,055	$ 12,960	$ 12,394	$ 12,413
Flat-rolled aluminum
Product Information [Line Items]
Sales revenue, goods, net									4,992	4,864	5,253
Fastening systems and rings
Product Information [Line Items]
Sales revenue, goods, net									2,102	2,060	2,168
Investment castings
Product Information [Line Items]
Sales revenue, goods, net									1,983	1,870	1,812
Other extruded and forged products
Product Information [Line Items]
Sales revenue, goods, net									1,565	1,495	1,332
Architectural aluminum systems
Product Information [Line Items]
Sales revenue, goods, net									1,065	1,010	951
Aluminum wheels
Product Information [Line Items]
Sales revenue, goods, net									805	689	790
Other
Product Information [Line Items]
Sales revenue, goods, net									$ 448	$ 406	$ 107

Segment and Geographic Area I97

Segment and Geographic Area Information - Schedule of Geographic Information for Sales (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales revenue, goods, net	$ 3,271	$ 3,236	$ 3,261	$ 3,192	$ 2,967	$ 3,138	$ 3,234	$ 3,055	$ 12,960	$ 12,394	$ 12,413
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales revenue, goods, net									8,167	7,823	8,044
France
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales revenue, goods, net									965	930	802
Hungary
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales revenue, goods, net									739	619	622
United Kingdom
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales revenue, goods, net									721	711	698
China
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales revenue, goods, net									615	582	565
Russia
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales revenue, goods, net									500	433	455
Germany
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales revenue, goods, net									309	284	264
Brazil
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales revenue, goods, net									285	250	297
Canada
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales revenue, goods, net									261	262	180
Japan
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales revenue, goods, net									141	145	138
Italy
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales revenue, goods, net									37	127	139
Other
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales revenue, goods, net									$ 220	$ 228	$ 209

Segment and Geographic Area I98

Segment and Geographic Area Information - Schedule of Geographic Information for Long-Lived Assets (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	$ 5,594	$ 5,499
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	4,005	3,966
China
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	347	336
Russia
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	276	295
United Kingdom
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	259	232
Hungary
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	227	194
France
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	159	118
Germany
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	88	64
Canada
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	63	58
Brazil
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	62	97
Other
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	$ 108	$ 139

Preferred and Common Stock - Ad

Preferred and Common Stock - Additional Information (Detail)	Oct. 02, 2017$ / sharesshares	Oct. 05, 2016$ / sharesshares	Aug. 31, 2016shares	Jul. 23, 2015shares	Jul. 22, 2015shares	Aug. 31, 2016shares	Aug. 31, 2016USD ($)shares	Aug. 30, 2016USD ($)	Jul. 31, 2015USD ($)$ / sharesshares	Sep. 30, 2014USD ($)$ / sharesshares	Dec. 31, 2017USD ($)$ / sharesshares	Sep. 30, 2017$ / shares	Jun. 30, 2017$ / sharesshares	Mar. 31, 2017$ / shares	Dec. 31, 2016USD ($)$ / sharesshares	Sep. 30, 2016$ / shares	Jun. 30, 2016$ / shares	Mar. 31, 2016$ / shares	Sep. 30, 2015$ / shares	Jun. 30, 2015$ / shares	Mar. 31, 2015$ / shares	Dec. 31, 2017USD ($)class_of_stock$ / sharesshares	Dec. 31, 2016USD ($)$ / sharesshares	Dec. 31, 2015USD ($)$ / sharesshares	Oct. 04, 2016shares	Dec. 31, 2014shares
Class of Stock [Line Items]
Preferred stock, number of classes | class_of_stock																						2
Preferred stock par value (usd per share) | $ / shares										$ 1
Public offering of preferred stock										$ 1,250,000,000
Depository shares sold (in shares) | shares	24,022									25,000,000			12,958,767
Proceeds from public offering										$ 1,213,000,000
Interest in preferred stock	0.10									0.10
Conversion of stock, shares converted (in shares) | shares	31,420
Reverse stock split ratio		0.3333
Common stock outstanding (in shares) | shares		400,000,000									481,416,537				438,519,780							481,416,537	438,519,780	1,310,160,141	1,300,000,000	1,216,663,661
Common stock, par value per share (usd pe share) | $ / shares		$ 1
Common stock decrease																							$ 877,000,000
Additional capital increase (decrease)																							877,000,000
Common stock authorized (in shares) | shares		600,000,000																							1,800,000,000
Treasury stock retirement (in shares) | shares			25,000,000			76,000,000	76,000,000
Retirement of treasury stock								$ 76,000,000															0
Treasury stock, value											$ 0				$ 0							$ 0	$ 0
Common stock issued (in shares) | shares											481,416,537											481,416,537
Dividends paid per share (usd per share) | $ / shares											$ 0.06	$ 0.06	$ 0.06	$ 0.06	$ 0.09	$ 0.09	$ 0.09	$ 0.09	$ 0.09	$ 0.09	$ 0.09			$ 0.36
Common stock, dividends yield (usd per share) | $ / shares											$ 0.06											$ 0.24	$ 0.36	$ 0.12
Document Fiscal Year Focus																						2,017
Common stock reserved for future issuance (in shares) | shares											47,000,000											47,000,000
Common stock, number of shares available for grant | shares											43,000,000											43,000,000
Stock based compensation expense, before tax																						$ 54,000,000	$ 76,000,000	$ 77,000,000
Stock based compensation expense, after tax																						$ 36,000,000	$ 51,000,000	$ 51,000,000
Stock based compensation expense, stock awards percentage																						85.00%	80.00%	80.00%
Unrecognized compensation costs on non-vested stock option awards (pretax)											$ 0				$ 0							$ 0	$ 0	$ 0
Unrecognized compensation costs on non-vested stock option grants (pretax)											43,000,000											$ 43,000,000
Unrecognized compensation costs on non-vested awards, weighted average period of recognition in years																						1 year 7 months 6 days
Expense related to the acceleration of expense related to retirement-eligible employees																						$ 15,000,000	$ 19,000,000	$ 15,000,000
Weighted average FMV per award, Granted (in usd per share) | $ / shares																						$ 21.86
Average risk-free interest rate																						2.40%
Share-based compensation arrangement by share-based payment award, options, grants in period, weighted average grant date fair value | $ / shares																						$ 6.26	$ 4.78	$ 10.07
Volatility																						38.10%	44.50%	36.50%
Dividend yield																						1.20%
Annual pre- and post-vesting forfeitures																						6.00%
Exercise behavior																						59.00%
Life (years)																						5 years 10 months 24 days
Number of options, Outstanding weighted average remaining contractual life																						5 years 3 months 29 days
Total intrinsic value of options outstanding											$ 53,000,000											$ 53,000,000
Stock options vested (in shares) | shares																						7,400,000
Stock option exercisable | shares																						8,900,000
Weighted average remaining contractual life, vested and exercisable																						4 years 1 month 28 days
Weighted average exercise price, vested and exercisable (in usd per share) | $ / shares											$ 25.90											$ 25.90
Total intrinsic value of options vested and exercisable											$ 26,000,000											$ 26,000,000
Proceeds from exercise of employee stock options																						50,000,000	$ 4,000,000	$ 25,000,000
Total tax benefit realized from these exercises																						4,000,000	0	6,000,000
Total intrinsic value of options exercised																						13,000,000	1,000,000	19,000,000
Restructuring and Other Charges
Class of Stock [Line Items]
Stock based compensation expense, before tax																						$ (13,000,000)
Stock Options
Class of Stock [Line Items]
Stock options granted, vesting period																						3 years
Share-based compensation arrangement by share-based payment award, expiration period																						10 years
Stock option exercisable | shares																						2,000,000
Restricted Stock Units (RSUs)
Class of Stock [Line Items]
Stock options granted, contractual term																						3 years
Share-based compensation arrangement by share-based payment award, award performance period																						3 years
Performance Shares
Class of Stock [Line Items]
Share-based compensation arrangement by share-based payment award, award performance period																						3 years
Weighted average FMV per award, Granted (in usd per share) | $ / shares																						$ 21.99
Average risk-free interest rate																						1.50%
Volatility																						38.00%
RTI
Class of Stock [Line Items]
Number of common stock shares issued in a part of acquisition (in shares) | shares		29,000,000		87,397,414	29,132,471				29,132,471																87,000,000
Number of shares to be issued upon conversion | $ / shares											$ 14,294,000											$ 14,294,000
Debt instrument, convertible, conversion price | $ / shares									$ 2.8315
RTI | Convertible Notes
Class of Stock [Line Items]
Debt instrument, convertible, conversion price | $ / shares									$ 28.1596
Debt instrument, amount received upon maturity per one thousand dollars in principal amount of notes held									$ 1,000
RTI | Tranche Due December 2015
Class of Stock [Line Items]
Long-term debt due within one year									115,000,000
RTI | Tranche Due October 2019
Class of Stock [Line Items]
Long-term debt due within one year									$ 403,000,000															$ 403,000,000
RTI | 1.63% Convertible Notes, Due 2019 | Convertible Notes
Class of Stock [Line Items]
Debt instrument, convertible, conversion rate per bond											0.0355119											0.0355119
Debt instrument, convertible, conversion price | $ / shares											$ 28.1596											$ 28.1596
Common stock
Class of Stock [Line Items]
Retirement of treasury stock							$ 76,000,000	76,000,000															76,000,000
Number of common stock shares issued in a part of acquisition (in shares) | shares																								87,397,414
Additional capital
Class of Stock [Line Items]
Retirement of treasury stock							$ 2,563,000,000	$ 2,563,000,000															$ 2,563,000,000
Class B Mandatory Convertible Preferred Stock
Class of Stock [Line Items]
Percentage ownership										5.375%
Mandatory convertible preferred stock
Class of Stock [Line Items]
Depository shares sold (in shares) | shares	24,975,978
Preferred stock liquidation preference (usd per share) | $ / shares										$ 500
Preferred shares (in shares) | shares										2,500,000
Interest in preferred stock	0.1
Preferred stock conversion price (in usd per share) | $ / shares	$ 1.56996
Conversion of stock, shares converted (in shares) | shares	39,211,286
Preferred Class A
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares) | shares											660,000											660,000
Preferred stock par value (usd per share) | $ / shares											$ 100											$ 100
Preferred stock dividend declared (usd per share) | $ / shares																						$ 3.75	$ 3.75	$ 3.75
Preferred stock, shares outstanding (in shares) | shares											546,024				546,024							546,024	546,024
Preferred Class B
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares) | shares											10,000,000											10,000,000
Preferred stock par value (usd per share) | $ / shares											$ 1											$ 1
Preferred stock dividend declared (usd per share) | $ / shares																						$ 20.1563	$ 26.875	$ 26.8750
Preferred stock, shares outstanding (in shares) | shares											0				2,500,000							0	2,500,000
Preferred stock, dividends, per share, cash paid | $ / shares																						$ 20.1563
Share-based Compensation Award, Tranche One | Stock Options
Class of Stock [Line Items]
Share-based compensation arrangement by share-based payment award, award vesting rights, percentage																						33.33%
Share-based Compensation Award, Tranche Two | Stock Options
Class of Stock [Line Items]
Share-based compensation arrangement by share-based payment award, award vesting rights, percentage																						33.33%
Share-based Compensation Award, Tranche Three | Stock Options
Class of Stock [Line Items]
Share-based compensation arrangement by share-based payment award, award vesting rights, percentage																						33.33%
Twenty Seventeen Awards | Performance Shares
Class of Stock [Line Items]
Stock options granted, vesting period																						3 years
Twenty Fifteen And Twenty Sixteen Awards | Share-based Compensation Award, Tranche One | Performance Shares
Class of Stock [Line Items]
Share-based compensation arrangement by share-based payment award, award vesting rights, percentage																						33.33%
Twenty Fifteen And Twenty Sixteen Awards | Share-based Compensation Award, Tranche Two | Performance Shares
Class of Stock [Line Items]
Share-based compensation arrangement by share-based payment award, award vesting rights, percentage																						33.33%
Twenty Fifteen And Twenty Sixteen Awards | Share-based Compensation Award, Tranche Three | Performance Shares
Class of Stock [Line Items]
Share-based compensation arrangement by share-based payment award, award vesting rights, percentage																						33.33%

Preferred and Common Stock - Sc

Preferred and Common Stock - Schedule of Share Activity (Detail) - shares	Oct. 05, 2016	Aug. 31, 2016	Aug. 31, 2016	Aug. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Treasury stock, beginning balance (in shares)					0	81,051,103	87,150,169
Common stock outstanding, beginning balance (in shares)	1,300,000,000				438,519,780	1,310,160,141	1,216,663,661
Treasury stock retirement (in shares)		(25,000,000)	(76,000,000)	(76,000,000)
Treasury stock, ending balance (in shares)					0	0	81,051,103
Common stock outstanding, ending balance (in shares)	400,000,000				481,416,537	438,519,780	1,310,160,141
Treasury stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issued for stock-based compensation plans (in shares)						5,219,660	6,099,066
Treasury stock retirement (in shares)						(75,831,443)
Common stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issued for stock-based compensation plans (in shares)					3,654,051	5,302,128	6,099,066
Number of common stock shares issued in a part of acquisition (in shares)							87,397,414
Reverse stock split (in shares)						(876,942,489)
Conversion of convertible notes (in shares)					39,242,706

Preferred and Common Stock -101

Preferred and Common Stock - Schedule of Activity for Stock Options and Stock Awards (Detail) shares in Thousands	12 Months Ended
	Dec. 31, 2017$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Number of options, Exercised (in shares)	(8,900)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Number of awards, Outstanding beginning of year (in shares)	8,000
Number of awards, Granted (in shares)	3,000
Number of awards, Exercised (in shares)	0
Number of awards, Converted (in shares)	(2,000)
Number of awards, Expired or forfeited (in shares)	(2,000)
Number of awards, Performance share adjustment (in shares)	0
Number of awards, Outstanding end of year (in shares)	7,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Weighted average FMV per award, Outstanding beginning of year (in usd per share) | $ / shares	$ 22.26
Weighted average FMV per award, Granted (in usd per share) | $ / shares	21.86
Weighted average FMV per award, Exercised (in usd per share) | $ / shares	0
Weighted average FMV per award, Converted (in usd per share) | $ / shares	24.95
Weighted average FMV per award, Expired or forfeited (in usd per share) | $ / shares	21.26
Weighted average FMV per award, Performance share adjustment (in usd per share) | $ / shares	21.48
Weighted average FMV per award, Outstanding, end of year (in usd per share) | $ / shares	$ 21.49
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Number of options, Outstanding beginning of year (in shares)	13,000
Number of options, Granted (in shares)	2,000
Number of options, Exercised (in shares)	(2,000)
Number of options, Converted (in shares)	0
Number of options, Expired or forfeited (in shares)	(2,000)
Number of options, Performance share adjustment (in shares)	0
Number of options, Outstanding end of year (in shares)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Weighted average exercise price, Outstanding beginning of year (in usd per share) | $ / shares	$ 24.14
Weighted average exercise price, granted (in usd per share) | $ / shares	21.13
Weighted average exercise price, exercised (in usd per share) | $ / shares	20.65
Weighted average exercise price, Converted (in usd per share) | $ / shares	0
Weighted average exercise price, expired or forfeited (in usd per share) | $ / shares	25.99
Weighted average exercise price, Performance share adjustment (in usd per share) | $ / shares	0
Weighted average exercise price Outstanding, end of year (in usd per share) | $ / shares	$ 23.94

Earnings Per Share - Reconcilia

Earnings Per Share - Reconciliation of Information Used to Compute Basic and Diluted EPS (Detail) - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Earnings Per Share [Abstract]
Net loss from continuing operations attributable to Arconic	$ (74)	$ (1,062)	$ (156)
Net income from continuing operations attributable to noncontrolling interests	0	0	(1)
Less: preferred stock dividends declared	(53)	(69)	(69)
Loss from continuing operations available to Arconic common shareholders	(127)	(1,131)	(226)
Income (loss) from discontinued operations after income taxes and noncontrolling interests	0	121	(165)
Net loss available to Arconic common shareholders—basic	(127)	(1,010)	(391)
Add: interest expense related to convertible notes		0	0	$ 0
Add: dividends related to mandatory convertible preferred stock		0	0	$ 0
Net loss available to Arconic common shareholders—diluted	$ (127)	$ (1,010)	$ (391)
Average shares outstanding-basic (in shares)	451	438	420
Stock options (in shares)		0	0	0
Stock and performance awards (in shares)	0	0	0
Mandatory convertible preferred stock (in shares)		0	0	0
Convertible notes (in shares)		0	0	0
Average shares outstanding-diluted (in shares)	451	438	420

Earnings Per Share - Additional

Earnings Per Share - Additional Information (Detail) - $ / shares shares in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Weighted Average
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of anti-dilutive securities (in shares)			5
Mandatory Convertible Notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of anti-dilutive securities (in shares)	39	39	26
Shares that would have been included in diluted earnings per share calculation (in shares)	30	28	26
Convertible Notes
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of anti-dilutive securities (in shares)	14	14
Shares that would have been included in diluted earnings per share calculation (in shares)	14	10	5
Stock Options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of anti-dilutive securities (in shares)	11	13	11
Shares that would have been included in diluted earnings per share calculation (in shares)	1	1	1
Weighted average exercise price of options (usd per share)	$ 33.32	$ 26.93	$ 38.25
Stock Awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of anti-dilutive securities (in shares)	7	8	7
Shares that would have been included in diluted earnings per share calculation (in shares)	5	4	4
Equity Unit Purchase Agreements
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Number of anti-dilutive securities (in shares)	3	10	9

Income Taxes - Components of In

Income Taxes - Components of Income from Continuing Operations Before Income Taxes (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
United States	$ 500	$ 84	$ 124
Foreign	(30)	330	59
Income from continuing operations before income taxes	$ 470	$ 414	$ 183

Income Taxes - Schedule of Prov

Income Taxes - Schedule of Provision for Income Taxes on Income from Continuing Operations (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current:
Federal	$ 0	$ 0	$ 0
Foreign	98	133	115
State and local	(2)	1	(1)
Current provision for income taxes, total	96	134	114
Deferred:
Federal	489	1,208	196
Foreign	37	136	29
State and local	(78)	(2)	0
Deferred provision for income taxes, total	448	1,342	225
Total	$ 544	$ 1,476	$ 339

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	Jul. 12, 2014	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Contingency [Line Items]
Tax benefit (charge) realized from exercise of employee stock options				$ (1,000,000)	$ 0	$ 2,000,000
Unamortized tax-deductible goodwill resulting from intercompany stock sales and reorganizations				$ 24,000,000
Unamortized tax-deduction rate on goodwill				25.00%
Tax cuts and jobs act of 2017, incomplete accounting, provisional income tax expense (benefit)		$ 272,000,000
Percentage of temporary tax differences that reverse within the carryforward period					30.00%
Percentage of deferred tax asset exclusive of reversing temporary differences					70.00%
Increase (decrease) to valuation allowance			$ 1,267,000,000	$ 831,000,000	$ 772,000,000	180,000,000
Valuation allowance		2,584,000,000	1,940,000,000	2,584,000,000	1,940,000,000	$ 1,291,000,000	$ 1,151,000,000
Tax credit carryforward, valuation allowance		379,000,000		379,000,000
Net deferred tax assets other		(24,000,000)	(164,000,000)	$ (24,000,000)	$ (164,000,000)
Percentage of tax rate decreased				52.50%	(15.70%)	(1.00%)
Percentage of the effect of unrecognized tax benefit, if recorded				15.00%	6.00%	7.00%
Interest or penalties recognized				$ 1,000,000	$ 0	$ 0
Income related to accrued interest and penalties				2,000,000	0	1,000,000
Amount accrued for payment of interest and penalties		2,000,000	2,000,000	2,000,000	2,000,000
Alcoa Corporation
Income Tax Contingency [Line Items]
Deferred tax assets, tax credit carryforwards, foreign, expired during period					302,000,000
Discrete income tax charge for valuation allowances					1,267,000,000
Net deferred tax assets other			(2,000,000)		(2,000,000)
State and Local Jurisdiction
Income Tax Contingency [Line Items]
Increase (decrease) to valuation allowance				98,000,000
Valuation allowance		750,000,000		750,000,000
Foreign Tax Authority
Income Tax Contingency [Line Items]
Foreign tax credits carry forward period	10 years
Tax credit carryforward, valuation allowance		302,000,000		302,000,000		134,000,000
Deferred tax assets, tax credit carryforwards, foreign, expired during period				57,000,000	128,000,000	15,000,000
Iceland And Suriname
Income Tax Contingency [Line Items]
Discrete income tax charge for valuation allowances						141,000,000
Suriname
Income Tax Contingency [Line Items]
Valuation allowance						$ 85,000,000
Suriname | Minimum
Income Tax Contingency [Line Items]
Foreign tax credits expiry period						2,016
Suriname | Maximum
Income Tax Contingency [Line Items]
Foreign tax credits expiry period						2,022
Iceland
Income Tax Contingency [Line Items]
Valuation allowance						$ 56,000,000
Iceland | Minimum
Income Tax Contingency [Line Items]
Foreign tax credits expiry period						2,017
Iceland | Maximum
Income Tax Contingency [Line Items]
Foreign tax credits expiry period						2,023
Internal Revenue Service IRS | Alcoa Corporation
Income Tax Contingency [Line Items]
Net deferred tax assets			925,000,000		925,000,000
Luxembourg
Income Tax Contingency [Line Items]
Valuation allowance			280,000,000		280,000,000
Discrete income tax charge for valuation allowances					42,000,000
Luxembourg | Alcoa Corporation
Income Tax Contingency [Line Items]
Net deferred tax assets			42,000,000		42,000,000
Federal Tax Services of Russia
Income Tax Contingency [Line Items]
Net deferred tax assets			19,000,000		19,000,000
Canada Revenue Agency
Income Tax Contingency [Line Items]
Net deferred tax assets			20,000,000		20,000,000
Australia
Income Tax Contingency [Line Items]
Valuation allowance			93,000,000		93,000,000
Tax Authority, Spain
Income Tax Contingency [Line Items]
Valuation allowance			$ 163,000,000		$ 163,000,000
Tax Authority, Spain | Foreign Tax Authority
Income Tax Contingency [Line Items]
Increase (decrease) to valuation allowance				675,000,000
Excess Foreign Tax Credits
Income Tax Contingency [Line Items]
Tax credit carryforward, valuation allowance		23,000,000		23,000,000
Tax Credits, Other Adjustments
Income Tax Contingency [Line Items]
Tax credit carryforward, valuation allowance		$ (14,000,000)		$ (14,000,000)

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of U.S. Federal Statutory Rate to Arconic's Effective Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
U.S. federal statutory rate	35.00%	35.00%	35.00%
Taxes on foreign operations	(7.50%)	(10.20%)	2.50%
Federal benefit of state tax	3.10%	0.40%	0.30%
Permanent differences on restructuring and other charges and asset disposals	(167.40%)	(107.80%)	3.60%
Non-deductible acquisition costs	0.30%	8.40%	7.10%
Statutory tax rate and law changes	52.50%	(15.70%)	(1.00%)
Tax holidays	(3.00%)	(0.80%)	(3.90%)
Tax credits	(0.70%)	(1.20%)	(2.80%)
Changes in valuation allowances	137.90%	426.80%	145.80%
Impairment of goodwill	53.50%	0.00%	4.80%
Company-owned life insurance/split-dollar net premiums	(0.00%)	23.00%	(3.00%)
Changes in uncertain tax positions	10.10%	2.10%	(2.20%)
Other	1.90%	(3.50%)	(1.00%)
Effective tax rate	115.70%	356.50%	185.20%

Income Taxes - Schedule of Comp

Income Taxes - Schedule of Components of Net Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Deferred tax assets, depreciation	$ 31	$ 15
Deferred tax assets, employee benefits	936	1,382
Deferred tax assets, loss provisions	134	181
Deferred tax assets, deferred income	19	20
Deferred tax assets, tax loss carryforwards	3,305	1,540
Deferred tax assets, tax credit carryforwards	638	652
Deferred tax assets, other	24	164
Deferred tax assets, gross	5,087	3,954
Valuation allowance	(2,584)	(1,940)	$ (1,291)	$ (1,151)
Deferred tax assets, net	2,503	2,014
Deferred tax liabilities, depreciation	693	817
Deferred tax liabilities, employee benefits	23	8
Deferred tax liabilities, loss provisions	14	1
Deferred tax liabilities, deferred expense	1,144	74
Deferred tax liabilities, tax loss carryforwards	0	0
Deferred tax liabilities, tax credit carryforwards	0	0
Deferred tax liabilities, other	33	19
Deferred tax liabilities, gross	1,907	919
Deferred tax liabilities, valuation allowance	0	0
Deferred tax liabilities, net	$ 1,907	$ 919

Income Taxes - Schedule of Expi

Income Taxes - Schedule of Expiration Periods of Deferred Tax Assets (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Tax Credit Carryforward [Line Items]
Tax loss carryforwards	$ 3,305
Tax credit carryforwards	638
Other	1,144
Valuation allowance	(2,584)	$ (1,940)	$ (1,291)	$ (1,151)
Deferred tax assets, net	2,503	$ 2,014
Expires within 10 years
Tax Credit Carryforward [Line Items]
Tax loss carryforwards	81
Tax credit carryforwards	531
Other	0
Valuation allowance	(467)
Deferred tax assets, net	145
Expires within 11-20 years
Tax Credit Carryforward [Line Items]
Tax loss carryforwards	781
Tax credit carryforwards	97
Other	0
Valuation allowance	(646)
Deferred tax assets, net	232
No expiration
Tax Credit Carryforward [Line Items]
Tax loss carryforwards	2,443
Tax credit carryforwards	10
Other	84
Valuation allowance	(1,376)
Deferred tax assets, net	1,161
Other
Tax Credit Carryforward [Line Items]
Tax loss carryforwards	0
Tax credit carryforwards	0
Other	1,060
Valuation allowance	(95)
Deferred tax assets, net	$ 965

Income Taxes - Schedule of Chan

Income Taxes - Schedule of Changes in Valuation Allowance (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Balance at beginning of year		$ 1,940	$ 1,291	$ 1,151
Increase to allowance	$ 1,267	831	772	180
Release of allowance		(246)	(209)	(42)
Acquisitions and divestitures (F)		(1)	(1)	29
Tax apportionment, tax rate and tax law changes		(24)	106	(15)
Foreign currency translation		84	(19)	(12)
Balance at end of year	$ 1,940	$ 2,584	$ 1,940	$ 1,291

Income Taxes - Reconciliatio111

Income Taxes - Reconciliation of Unrecognized Tax Benefits (Excluding Interest and Penalties) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Balance at beginning of year	$ 28	$ 18	$ 7
Additions for tax positions of the current year	23	12	0
Additions for tax positions of prior years	27	0	14
Reductions for tax positions of prior years	0	0	(2)
Settlements with tax authorities	0	(1)	0
Expiration of the statute of limitations	(5)	(1)	(1)
Foreign currency translation	0	0	0
Balance at end of year	$ 73	$ 28	$ 18

Receivables - Additional Inform

Receivables - Additional Information (Detail)	Mar. 30, 2012USD ($)	Dec. 31, 2017USD ($)financial_institution	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2017USD ($)
Schedule Of Financial Receivables [Line Items]
Number of arrangement with different financial institution to sell customer receivables | financial_institution		3
Funding of customer receivables sold		$ 0	$ 100,000,000
Sale of customer receivables	$ 304,000,000
Cash received for receivables	50,000,000
Deferred purchase price receivable	$ 254,000,000	187,000,000	83,000,000
Net cash funding received during the period		300,000,000
Amount of cash draws under arrangement during the period		2,358,000,000
Amount of cash repayments under arrangement during the period		(2,058,000,000)		$ 0
Amount of cash draws under arrangement since inception		600,000,000	500,000,000
Amount of cash repayments under arrangement since inception		(600,000,000)	(400,000,000)
Gross cash outflows from deferred purchased receivables		5,471,000,000	(5,367,000,000)		$ 35,409,000,000
Gross cash inflows from deferred purchased receivables		5,340,000,000	$ (5,406,000,000)
Cash collections of other receivables					$ (34,872,000,000)
Minimum
Schedule Of Financial Receivables [Line Items]
Funding of customer receivables sold		200,000,000
Maximum
Schedule Of Financial Receivables [Line Items]
Funding of customer receivables sold		$ 400,000,000

Receivables - Schedule of Allow

Receivables - Schedule of Allowance for Doubtful Accounts (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Customer receivables
Allowance for Doubtful Accounts Receivable [Roll Forward]
Balance at beginning of year	$ 13	$ 8	$ 6
Provision for doubtful accounts	1	7	4
Write off of uncollectible accounts	(5)	(3)	(2)
Recoveries of prior write-offs	0	(1)	0
Other	(1)	2	0
Balance at end of year	8	13	8
Other receivables
Allowance for Doubtful Accounts Receivable [Roll Forward]
Balance at beginning of year	32	34	24
Provision for doubtful accounts	9	6	8
Write off of uncollectible accounts	(1)	(1)	2
Recoveries of prior write-offs	(3)	1	(1)
Other	(3)	(8)	1
Balance at end of year	$ 34	$ 32	$ 34

Interest Cost Components - Sche

Interest Cost Components - Schedule of Interest Cost Components (Detail) - USD ($) $ in Millions	Jun. 19, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Debt Disclosure [Abstract]
Amount charged to expense	$ 24	$ 496	$ 499	$ 473
Amount capitalized		22	32	27
Interest costs		$ 518	$ 531	$ 500

Pension and Other Postretire115

Pension and Other Postretirement Benefits - Additional Information (Detail) - USD ($)	Apr. 01, 2018	Apr. 18, 2017	Aug. 01, 2016	Sep. 30, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Average duration refined yield curve model parallels the plans, years						11 years
Rate of compensation increase						3.50%	3.50%	3.50%
Average period of historical returns used to calculate expected future returns, in years						5 years
Decrease in expected long-term rate of return						0.75%		0.25%
Pension and other postretirement plans, expected long-term rate of return, average of actual results, period of measurement						20 years
Expected long term rate of return on plan assets						7.75%	7.75%	7.75%
Health care cost trend rate assumed for next year						5.50%	5.50%	5.50%
Number of years over actual annual health care cost trend experience						3 years
Health care cost trend rate						4.50%	4.50%	4.50%
Cash contribution to pension plans						$ 310,000,000	$ 290,000,000	$ 470,000,000
Minimum required cash contribution to pension plan				$ 50,000,000		350,000,000
Aggregate cash cash contribution to pension plan				$ 150,000,000
Cash contribution term to pension plan				30 months
Employer contributions		$ 50,000,000
Expenses related to saving and investment plans						$ 89,000,000	71,000,000	83,000,000
Maximum
Defined Benefit Plan Disclosure [Line Items]
Health care cost trend rate						9.00%
Minimum
Defined Benefit Plan Disclosure [Line Items]
Health care cost trend rate						2.20%
Scenario, Forecast
Defined Benefit Plan Disclosure [Line Items]
Expected long term rate of return on plan assets					7.00%
Pension benefits
Defined Benefit Plan Disclosure [Line Items]
Accumulated (increase) decrease in net actuarial loss after-tax, plan amendment						$ 0	0	(9,000,000)
Rate of compensation increase						3.50%
Average period over which rate of compensation increases, years						5 years
Change in interest cost component of net periodic benefit cost determination						$ 34,000,000	84,000,000
Employer contributions						310,000,000	296,000,000
Other postretirement benefits
Defined Benefit Plan Disclosure [Line Items]
Accumulated (increase) decrease in net actuarial loss after-tax, plan amendment						0	0	$ 4,000,000
Change in interest cost component of net periodic benefit cost determination						6,000,000	14,000,000
Employer contributions						0	$ 0
United Steelworkers Labor Agreement
Defined Benefit Plan Disclosure [Line Items]
Increase in pension liability, plan amendment			$ 845,000,000
Accumulated (increase) decrease in net actuarial loss after-tax, plan amendment			$ (551,000,000)
United States
Defined Benefit Plan Disclosure [Line Items]
Minimum required cash contribution to pension plan						$ 320,000,000
Subsequent Event | Salaried And Retirement Savings Plan
Defined Benefit Plan Disclosure [Line Items]
Retirement savings plan, employer contribution, percent	3.00%
Retirement savings plan, additional employer contribution, percent	3.00%

Pension and Other Postretire116

Pension and Other Postretirement Benefits - Schedule of Obligations and Funded Status (Detail) - USD ($) $ in Millions	Apr. 18, 2017	Dec. 31, 2017	Dec. 31, 2016
Change in plan assets
Employer contributions	$ 50
Pension benefits
Change in benefit obligation
Benefit obligation at beginning of year		$ 7,026	$ 14,247
Service cost		90	165
Interest cost		234	435
Amendments		1	2
Actuarial (gains) losses		311	770
Transfer to Alcoa Corporation		0	(7,577)
Settlements		0	(82)
Benefits paid, net of participants’ contributions		(425)	(794)
Medicare Part D subsidy receipts		0	0
Foreign currency translation impact		122	(140)
Benefit obligation at end of year		7,359	7,026
Change in plan assets
Fair value of plan assets at beginning of year		4,666	10,928
Actual return on plan assets		212	89
Employer contributions		310	296
Participants’ contributions		0	16
Benefits paid		(404)	(762)
Administrative expenses		(33)	(65)
Transfer to Alcoa Corporation		0	(5,610)
Settlements		0	(82)
Foreign currency translation impact		111	(144)
Fair value of plan assets at end of year		4,862	4,666
Defined Benefit Plan, Funded (Unfunded) Status of Plan [Abstract]
Funded status		(2,497)	(2,360)
Less: Amounts attributed to joint venture partners		0	0
Net funded status		(2,497)	(2,360)
Amounts recognized in the Consolidated Balance Sheet consist of:
Noncurrent assets		89	6
Current liabilities		(22)	(21)
Noncurrent liabilities		(2,564)	(2,345)
Net amount recognized		(2,497)	(2,360)
Amounts recognized in Accumulated Other Comprehensive Loss consist of:
Net actuarial loss		3,240	2,979
Prior service cost (benefit)		10	15
Total, before tax effect		3,250	2,994
Less: Amounts attributed to joint venture partners		0	0
Net amount recognized, before tax effect		3,250	2,994
Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Loss consist of:
Net actuarial loss (gain)		481	(1,992)
Amortization of accumulated net actuarial loss		(220)	(380)
Prior service (benefit) cost		0	(42)
Amortization of prior service (cost) benefit		(5)	(13)
Total, before tax effect		256	(2,427)
Less: Amounts attributed to joint venture partners		0	38
Net amount recognized, before tax effect		256	(2,389)
Other postretirement benefits
Change in benefit obligation
Benefit obligation at beginning of year		980	2,319
Service cost		7	13
Interest cost		30	63
Amendments		0	0
Actuarial (gains) losses		1	112
Transfer to Alcoa Corporation		0	(1,340)
Settlements		0	0
Benefits paid, net of participants’ contributions		(98)	(197)
Medicare Part D subsidy receipts		7	9
Foreign currency translation impact		0	1
Benefit obligation at end of year		927	980
Change in plan assets
Fair value of plan assets at beginning of year		0	0
Actual return on plan assets		0	0
Employer contributions		0	0
Participants’ contributions		0	0
Benefits paid		0	0
Administrative expenses		0	0
Transfer to Alcoa Corporation		0	0
Settlements		0	0
Foreign currency translation impact		0	0
Fair value of plan assets at end of year		0	0
Defined Benefit Plan, Funded (Unfunded) Status of Plan [Abstract]
Funded status		(927)	(980)
Less: Amounts attributed to joint venture partners		0	0
Net funded status		(927)	(980)
Amounts recognized in the Consolidated Balance Sheet consist of:
Noncurrent assets		0	0
Current liabilities		(86)	(91)
Noncurrent liabilities		(841)	(889)
Net amount recognized		(927)	(980)
Amounts recognized in Accumulated Other Comprehensive Loss consist of:
Net actuarial loss		146	150
Prior service cost (benefit)		(37)	(45)
Total, before tax effect		109	105
Less: Amounts attributed to joint venture partners		0	0
Net amount recognized, before tax effect		109	105
Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Loss consist of:
Net actuarial loss (gain)		1	(224)
Amortization of accumulated net actuarial loss		(5)	(24)
Prior service (benefit) cost		0	37
Amortization of prior service (cost) benefit		8	24
Total, before tax effect		4	(187)
Less: Amounts attributed to joint venture partners		0	0
Net amount recognized, before tax effect		4	(187)
United States | Pension benefits
Change in benefit obligation
Benefit obligation at beginning of year		5,707
Benefit obligation at end of year		6,018	5,707
Change in plan assets
Fair value of plan assets at beginning of year		3,495
Fair value of plan assets at end of year		3,544	3,495
Defined Benefit Plan, Funded (Unfunded) Status of Plan [Abstract]
Funded status		$ (2,474)	$ (2,212)

Pension and Other Postretire117

Pension and Other Postretirement Benefits - Schedule of Pension Plan Benefit Obligations (Detail) - Pension benefits - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	$ 7,359	$ 7,026	$ 14,247
Accumulated benefit obligation	7,169	6,850
The aggregate projected benefit obligation and fair value of plan assets for pension plans with projected benefit obligations in excess of plan assets was as follows:
Projected benefit obligation	6,600	6,995
Fair value of plan assets	4,016	4,629
The aggregate accumulated benefit obligation and fair value of plan assets for pension plans with accumulated benefit obligations in excess of plan assets was as follows:
Accumulated benefit obligation	6,422	6,104
Fair value of plan assets	$ 3,998	$ 3,894

Pension and Other Postretire118

Pension and Other Postretirement Benefits - Components of Net Periodic Benefit Cost (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pension benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 90	$ 155	$ 175
Interest cost	234	431	577
Expected return on plan assets	(332)	(677)	(753)
Recognized net actuarial loss	220	380	468
Amortization of prior service cost (benefit)	5	13	16
Settlements	0	19	16
Curtailments	0	0	9
Special termination benefits	0	2	16
Net periodic benefit cost	217	323	524
Discontinued operations	0	122	248
Net amount recognized in Statement of Consolidated Operations	217	201	276
Other postretirement benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	7	13	14
Interest cost	30	63	92
Expected return on plan assets	0	0	0
Recognized net actuarial loss	5	24	17
Amortization of prior service cost (benefit)	(8)	(24)	(37)
Settlements	0	0	0
Curtailments	0	0	(4)
Special termination benefits	0	0	0
Net periodic benefit cost	34	76	82
Discontinued operations	0	41	43
Net amount recognized in Statement of Consolidated Operations	34	35	39
Decrease in net periodic benefit cost for the recognition of the federal subsidy awarded under Medicare Part D	11	22	34
United States | Pension benefits
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost	$ 206	$ 261	$ 423

Pension and Other Postretire119

Pension and Other Postretirement Benefits - Schedule of Amounts Expected to be Recognized in Net Periodic Benefit Cost (Detail) $ in Millions	Dec. 31, 2017USD ($)
Pension benefits
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss recognition	$ 168
Prior service cost (benefit) recognition	3
Other postretirement benefits
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss recognition	9
Prior service cost (benefit) recognition	$ (8)

Pension and Other Postretire120

Pension and Other Postretirement Benefits - Schedule of Weighted Average Assumptions Used to Determine Benefit Obligations (Detail)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Discount rate	3.75%	4.20%
Rate of compensation increase	3.50%	3.50%
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount rate to calculate service cost	4.20%	4.29%	4.00%
Discount rate to calculate interest cost	3.60%	3.15%	4.00%
Expected long-term rate of return on plan assets	7.75%	7.75%	7.75%
Rate of compensation increase	3.50%	3.50%	3.50%

Pension and Other Postretire121

Pension and Other Postretirement Benefits - Schedule of Assumed Health Care Cost Trend Rates (Detail)	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Retirement Benefits [Abstract]
Health care cost trend rate assumed for next year	5.50%	5.50%	5.50%
Rate to which the cost trend rate gradually declines	4.50%	4.50%	4.50%

Pension and Other Postretire122

Pension and Other Postretirement Benefits - Schedule of One-Percentage Point Change in Assumed Rates of Health Care Cost Trend Rates (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)
Retirement Benefits [Abstract]
Effect on other postretirement benefit obligations, 1% increase	$ 29
Effect on total of service and interest cost components, 1% increase	1
Effect on other postretirement benefit obligations, 1% decrease	(28)
Effect on total of service and interest cost components, 1% decrease	$ (1)

Pension and Other Postretire123

Pension and Other Postretirement Benefits - Schedule of Pension and Postretirement Plans Investment Policy and Weighted Average Asset Allocations (Detail)	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, asset allocations	100.00%	100.00%
Equities
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, asset allocations	28.00%	30.00%
Equities | Maximum
Defined Benefit Plan Disclosure [Line Items]
Policy range	55.00%
Equities | Minimum
Defined Benefit Plan Disclosure [Line Items]
Policy range	20.00%
Fixed income
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, asset allocations	47.00%	42.00%
Fixed income | Maximum
Defined Benefit Plan Disclosure [Line Items]
Policy range	55.00%
Fixed income | Minimum
Defined Benefit Plan Disclosure [Line Items]
Policy range	25.00%
Other investments
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, asset allocations	25.00%	28.00%
Other investments | Maximum
Defined Benefit Plan Disclosure [Line Items]
Policy range	35.00%
Other investments | Minimum
Defined Benefit Plan Disclosure [Line Items]
Policy range	15.00%

Pension and Other Postretire124

Pension and Other Postretirement Benefits - Schedule of Fair Value of Pension Plan Assets (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Net receivables which represents assets related to divested businesses to be transferred to the buyers	$ 28	$ 20
Pension benefits
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	4,862	4,666	$ 10,928
Fair Value, Measurements, Recurring | Pension benefits
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	4,834	4,646
Defined benefit plan, alternative investments, fair value of plan asset	2,932	2,878
Fair Value, Measurements, Recurring | Pension benefits | Equities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	1,357	1,395
Defined benefit plan, alternative investments, fair value of plan asset	978	1,002
Fair Value, Measurements, Recurring | Pension benefits | Equities | Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	972	824
Defined benefit plan, alternative investments, fair value of plan asset	593	431
Fair Value, Measurements, Recurring | Pension benefits | Equities | Hedge Funds, Equity
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	230	406
Defined benefit plan, alternative investments, fair value of plan asset	230	406
Fair Value, Measurements, Recurring | Pension benefits | Equities | Private Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	155	165
Defined benefit plan, alternative investments, fair value of plan asset	155	165
Fair Value, Measurements, Recurring | Pension benefits | Fixed income
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	2,278	1,958
Defined benefit plan, alternative investments, fair value of plan asset	924	729
Fair Value, Measurements, Recurring | Pension benefits | Fixed income | Intermediate and Long Duration Government Credit
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	1,961	773
Defined benefit plan, alternative investments, fair value of plan asset	779	655
Fair Value, Measurements, Recurring | Pension benefits | Fixed income | Other Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	317	1,185
Defined benefit plan, alternative investments, fair value of plan asset	145	74
Fair Value, Measurements, Recurring | Pension benefits | Other investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	1,199	1,293
Defined benefit plan, alternative investments, fair value of plan asset	1,030	1,147
Fair Value, Measurements, Recurring | Pension benefits | Other investments | Other Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	359	243
Defined benefit plan, alternative investments, fair value of plan asset	275	178
Fair Value, Measurements, Recurring | Pension benefits | Other investments | Real Estate Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	257	266
Defined benefit plan, alternative investments, fair value of plan asset	172	185
Fair Value, Measurements, Recurring | Pension benefits | Other investments | Discretionary And Systematic Macro Hedge Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	583	784
Defined benefit plan, alternative investments, fair value of plan asset	583	784
Fair Value, Measurements, Recurring | Pension benefits | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	906	1,622
Fair Value, Measurements, Recurring | Pension benefits | Level 1 | Equities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	379	393
Fair Value, Measurements, Recurring | Pension benefits | Level 1 | Equities | Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	379	393
Fair Value, Measurements, Recurring | Pension benefits | Level 1 | Equities | Hedge Funds, Equity
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	0	0
Fair Value, Measurements, Recurring | Pension benefits | Level 1 | Equities | Private Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	0	0
Fair Value, Measurements, Recurring | Pension benefits | Level 1 | Fixed income
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	365	1,083
Fair Value, Measurements, Recurring | Pension benefits | Level 1 | Fixed income | Intermediate and Long Duration Government Credit
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	201	23
Fair Value, Measurements, Recurring | Pension benefits | Level 1 | Fixed income | Other Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	164	1,060
Fair Value, Measurements, Recurring | Pension benefits | Level 1 | Other investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	162	146
Fair Value, Measurements, Recurring | Pension benefits | Level 1 | Other investments | Other Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	77	65
Fair Value, Measurements, Recurring | Pension benefits | Level 1 | Other investments | Real Estate Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	85	81
Fair Value, Measurements, Recurring | Pension benefits | Level 1 | Other investments | Discretionary And Systematic Macro Hedge Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	0	0
Fair Value, Measurements, Recurring | Pension benefits | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	996	146
Fair Value, Measurements, Recurring | Pension benefits | Level 2 | Equities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	0	0
Fair Value, Measurements, Recurring | Pension benefits | Level 2 | Equities | Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	0	0
Fair Value, Measurements, Recurring | Pension benefits | Level 2 | Equities | Hedge Funds, Equity
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	0	0
Fair Value, Measurements, Recurring | Pension benefits | Level 2 | Equities | Private Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	0	0
Fair Value, Measurements, Recurring | Pension benefits | Level 2 | Fixed income
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	989	146
Fair Value, Measurements, Recurring | Pension benefits | Level 2 | Fixed income | Intermediate and Long Duration Government Credit
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	981	95
Fair Value, Measurements, Recurring | Pension benefits | Level 2 | Fixed income | Other Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	8	51
Fair Value, Measurements, Recurring | Pension benefits | Level 2 | Other investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	7	0
Fair Value, Measurements, Recurring | Pension benefits | Level 2 | Other investments | Other Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	7	0
Fair Value, Measurements, Recurring | Pension benefits | Level 2 | Other investments | Real Estate Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	0	0
Fair Value, Measurements, Recurring | Pension benefits | Level 2 | Other investments | Discretionary And Systematic Macro Hedge Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	$ 0	$ 0

Pension and Other Postretire125

Pension and Other Postretirement Benefits - Schedule of Benefit Payments Expected to be Paid and Expected Medicare Part D Subsidy Receipts (Detail) $ in Millions	Dec. 31, 2017USD ($)
Pension benefits
Defined Benefit Plan Disclosure [Line Items]
2,018	$ 435
2,019	440
2,020	440
2,021	445
2,022	450
Thereafter	2,265
Total benefit payments	4,475
Gross Other post- retirement benefits
Defined Benefit Plan Disclosure [Line Items]
2,018	90
2,019	90
2,020	90
2,021	90
2,022	90
Thereafter	335
Total benefit payments	785
Medicare Part D subsidy receipts
Defined Benefit Plan Disclosure [Line Items]
2,018	5
2,019	5
2,020	5
2,021	5
2,022	5
Thereafter	25
Total benefit payments	50
Net Other post- retirement benefits
Defined Benefit Plan Disclosure [Line Items]
2,018	85
2,019	85
2,020	85
2,021	85
2,022	85
Thereafter	310
Total benefit payments	$ 735

Other Financial Instruments - S

Other Financial Instruments - Schedule of Carrying Values and Fair Values of Other Financial Instruments (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Carrying Value
Derivative [Line Items]
Cash and cash equivalents	$ 2,150	$ 1,863
Restricted cash	4	15
Derivatives - current asset	61	14
Noncurrent receivables	20	21
Derivatives - noncurrent asset	33	10
Available-for-sale securities	106	102
Investment in common stock of Alcoa Corporation	0	1,020
Short-term borrowings	38	40
Derivatives - current liability	45	5
Commercial paper	0	0
Derivatives - noncurrent liability	14	3
Contingent payment related to an acquisition	0	78
Long-term debt, less amount due within one year	6,806	8,044
Fair Value
Derivative [Line Items]
Cash and cash equivalents	2,150	1,863
Restricted cash	4	15
Derivatives - current asset	61	14
Noncurrent receivables	20	21
Derivatives - noncurrent asset	33	10
Available-for-sale securities	106	102
Investment in common stock of Alcoa Corporation	0	1,020
Short-term borrowings	38	40
Derivatives - current liability	45	5
Commercial paper	0	0
Derivatives - noncurrent liability	14	3
Contingent payment related to an acquisition	0	78
Long-term debt, less amount due within one year	$ 7,443	$ 8,519

Subsequent Events - Additional

Subsequent Events - Additional Information (Details) - USD ($)	Apr. 01, 2018	Feb. 28, 2018	Dec. 31, 2017
5.72% Notes, due 2019
Subsequent Event [Line Items]
Convertible notes, interest rate			5.72%
Subsequent Event
Subsequent Event [Line Items]
Stock repurchase program, authorized amount		$ 500,000,000
Subsequent Event | 5.72% Notes, due 2019
Subsequent Event [Line Items]
Approved debt reduction amount		$ 500,000,000
Subsequent Event | Salaried And Retirement Savings Plan
Subsequent Event [Line Items]
Retirement savings plan, employer contribution, percent	3.00%
Retirement savings plan, additional employer contribution, percent	3.00%

Quarterly Data - Schedule of Qu

Quarterly Data - Schedule of Quarterly Data (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Sales revenue, goods, net	$ 3,271	$ 3,236	$ 3,261	$ 3,192	$ 2,967	$ 3,138	$ 3,234	$ 3,055	$ 12,960	$ 12,394	$ 12,413
Net income (loss) attributable to Arconic	$ (727)	$ 119	$ 212	$ 322	$ (1,258)	$ 166	$ 135	$ 16	$ (74)	$ (941)	$ (322)
Basic
Continuing operations (in usd per share)					$ (2.98)	$ 0.11	$ 0.08	$ 0.21	$ (0.28)	$ (2.58)	$ (0.54)
Discontinued operations (in usd per share)					0.07	0.23	0.19	(0.21)	0	0.27	(0.39)
Net loss per share-basic (in usd per share)	$ (1.51)	$ 0.23	$ 0.44	$ 0.69	(2.91)	0.34	0.27	0	(0.28)	(2.31)	(0.93)
Diluted
Continuing operations (in usd per share)					(2.98)	0.11	0.08	0.21	(0.28)	(2.58)	(0.54)
Discontinued operations (in usd per share)					0.07	0.22	0.19	(0.21)	0	0.27	(0.39)
Net loss per share-diluted (in usd per share)	$ (1.51)	$ 0.22	$ 0.43	$ 0.65	$ (2.91)	$ 0.33	$ 0.27	$ 0	$ (0.28)	$ (2.31)	$ (0.93)
Goodwill impairment									$ 719	$ 0	$ 25
Tax cuts and jobs act of 2017, incomplete accounting, provisional income tax expense (benefit)	$ 272
Disposal group, contingent liability, period increase (decrease), net of tax	18
Disposal group, contingent liability, period increase (decrease)	25
Increase to allowance					$ 1,267				831	772	$ 180
Firth Rixson
Diluted
Business combination, contingent consideration arrangements, change in amount of contingent consideration, liability, net of tax									81
Contingent consideration arrangements, change in amount of contingent consideration, liability	(81)				$ (56)				81	$ 56
Engineered Products and Solutions
Diluted
Goodwill, impairment loss, net of tax	719
Goodwill impairment	$ 719								$ 719